|
|
(One intermediate revision by the same user not shown) |
Line 1: |
Line 1: |
| {{Header}} | | {{Header}} |
| {{Ref-Nelsen1953}} | | {{Ref-Nelsen1953}} |
| | |
| | {{Nelsen1953 TOC}} |
| {{Historic Disclaimer}} | | {{Historic Disclaimer}} |
| =Part III The Development of Primitive Embryonic Form= | | =Part III The Development of Primitive Embryonic Form= |
Line 617: |
Line 619: |
|
| |
|
| c. Early Differentiation and Derivatives of the Hypomere | | c. Early Differentiation and Derivatives of the Hypomere |
|
| |
|
| |
| 1) Contributions of the Hypomere (I^ateral Plate Mesoderm) to the Developing Pharyngeal Area of the Gut Tube. The developing foregut (Chap.
| |
| 13) may be divided into four main areas, namely, (1) head gut, (2) pharyngeal, (3) esophageal, and (4) stomach areas. The head gut is small and
| |
| represents a pre-oral extension of the gut; the pharyngeal area is large and
| |
| expansive and forms about half of the forming foregut in the early embryo;
| |
| the esophageal segment is small and constricted; and the forming stomach
| |
| region is enlarged. At this point, however, concern is given specifically to the
| |
| developing foregut in relation to the early development of the pharyngeal
| |
| region.
| |
|
| |
| In the pharyngeal area the foregut expands laterally. Beginning at its anterior end, it sends outward a series of paired, pouch-like diverticula, known
| |
| as the branchial (pharyngeal or visceral) pouches. These pouches push outward toward the ectodermal (epidermal) layer. In doing so, they separate
| |
| the lateral plate mesoderm which synchronously has divided into columnar
| |
| masses or cells (fig. 252E, F). Normally, about four to six pairs of branchial
| |
| (pharyngeal) pouches are formed in gnathostomous vertebrates, although in
| |
| the cyclostomatous fish, Petromyzon, eight pairs appear. In the embryo of the
| |
| shark, Squalus acanthias, six pairs are formed, while in the amphibia, four
| |
| to six pairs of pouches may appear (fig. 252F). In the chick, pig, and human,
| |
| four pairs of pouches normally occur (figs. 259, 261). Also, invaginations or
| |
| inpushings of the epidermal layer occur, the branchial grooves (visceral furrows); the latter meet the entodermal outpocketings (figs. 252F; 262B).
| |
|
| |
| The end result of all these developmental movements in the branchial area
| |
| is to produce elongated, dorso-ventral, paired columns of mesodermal cells
| |
| (figs. 252E; 253), the visceral or branchial arches, which alternate with the
| |
| branchial-groove-pouch or gill-slit areas (figs. 252F; 253). The most anterior
| |
| pair of visceral arches forms the mandibular visceral arches; the second pair
| |
| forms the hyoid visceral arches; and the succeeding pairs form the branchial
| |
| (gill) arches (figs. 239C, D; 240; 244; 246; 252E; 253). The branchial arches
| |
| with their mesodermal columns of cells will, together with the contributions
| |
| from the neural crest cells referred to above, give origin to the connective,
| |
| muscle, and blood-vessel-forming tissues in this area.
| |
|
| |
|
| |
|
| |
| 528
| |
|
| |
|
| |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
|
| |
|
| |
| 2) Contributions of the Hypomere (Lateral Plate Mesoderm) to the Formation of the Gut Tube and Heart Structures. Throughout the length of the
| |
| forming gut tube, from the oral area to the anal region, the lateral plate mesoderm (mesoblast) contributes much to the forming gut tube. This is occasioned to a great extent posterior to the pharyngeal area by the fact that the
| |
| inner or mesial walls of the two hypomeres enswathe the forming gut tube
| |
| as they fuse in the median plane (fig. 241), forming the dorsal and ventral
| |
| mesenteries of the gut. However, in the heart area, due to the dorsal displacement of the foregut, the dorsal mesentery is vestigial or absent while
| |
| the ventral mesentery is increased in extent. Each mesial wall of the hypomeric
| |
| mesoderm, forming the ventral mesentery in the region of the developing
| |
| heart, becomes cupped around the primitive blood capillaries, coursing anteriad in this area to form the rudiments of the developing heart. The ventral
| |
| mesentery in the heart area thus gives origin to the dorsal mesocardium, the
| |
| ventral mesocardium, and the rudimentary, cup-shaped, cpimyocardial structures around the fusing blood capillaries (figs. 236C-D; 254A). The primitive
| |
| blood capillaries soon unite to form the rudiment of the future endocardium
| |
| of the heart, while the enveloping epimyocardium establishes the rudiment of
| |
| the future muscle and connective tissues of the heart (Chap. 17).
| |
|
| |
| On the other hand, in the region of the stomach and continuing posteriorly
| |
| to the anal area of the gut, the movement mediad of the mesial walls of the
| |
| two lateral plate (hypomeric) mesodermal areas occurs in such a way as to
| |
|
| |
|
| |
|
| |
| Fig. 253. Diagram illustrating the basic plan of the vertebrate head based upon the
| |
| shark, Scy Ilium canicula. (Modified from Goodrich: 1918, Quart. Jour. Micros. Science, 63.)
| |
|
| |
|
| |
|
| |
| CONTRIBUTIONS OF THE MESODERM TO PRIMITIVE BODY FORMATION
| |
|
| |
|
| |
| 529
| |
|
| |
|
| |
|
| |
| the hypomeres to the developing heart and gut structures in reptiles, birds, and mammals.
| |
| Sections are drawn through the following regions: (A) Through primitive tubular heart
| |
| anterior to sinus venosus. (B) Through caudal end of sinus venosus and lateral meso*
| |
| cardia. (C) Through liver region. (D) Through region posterior to liver. (E)
| |
| Through posterior trunk in region of urinary bladder.
| |
|
| |
| envelop or enclose the gut tube. This enclosure readily occurs because in this
| |
| region of the trunk, the gut tube lies closer to the ventral aspect of the embryo
| |
| than in the heart area. Consequently, a dorsal mesentery above and a ventral
| |
| mesentery below the primitive gut tube are formed (fig. 25 4C). The dorsal
| |
| and ventral mesenteries may not persist everywhere along the gut (fig. 254D).
| |
| The degree of persistence varies in different vertebrates; these variations will
| |
| be mentioned later (Chap. 20) when the coelomic cavities are discussed.
| |
| However, there is a persistence of the ventral mesentery below the stomach
| |
| and anterior intestinal area of all vertebrates, for here the ventral mesentery
| |
| (i.e., the two medial walls of the lateral plate mesoderm below the gut) contributes to the development of the liver and the pancreas. These matters are
| |
| discussed in Chapter 13.
| |
|
| |
| Aside from the formation of the dorsal and ventral mesenteries by the inward movement and fusion of the medial walls of the lateral plate mesoderm
| |
| above and below the primitive enteron or gut tube, that part of the medial
| |
| walls of the lateral plate mesoderm which envelops the primitive gut itself is
| |
| of great importance. This importance arises from the fact that the entoderm
| |
| of the gut only forms the lining tissue of the future digestive tract and its
| |
| various glands, such as the liver, pancreas, etc., whereas mesenchymal contributions from the medial wall of the lateral plate mesoderm around the
| |
|
| |
|
| |
|
| |
| 530
| |
|
| |
|
| |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
|
| |
|
| |
| entodermal lining give origin to smooth muscle tissue, connective tissue, etc.
| |
| (figs. 254C, D; 258; 260; 262; 278C). It is apparent, therefore, that the gut
| |
| throughout its length is formed from two embryonic contributions, namely,
| |
| one from the entoderm and the other from the mesenchyme given off by the
| |
| medial walls of the lateral plate or hypomeric mesoderm.
| |
|
| |
| {Note: The word splanchnic is an adjective and is derived from a Greek
| |
| word meaning entrails or bowels. That is, it pertains to the soft structures
| |
| within the body wall. The plural noun viscera (singular, viscus) is derived
| |
| from the Latin and signifies the same structures, namely, the heart, liver,
| |
| stomach, intestine, etc., which lie within the cavities of the body. It is fitting,
| |
| therefore, to apply the adjective splanchnic to the medial portion of the hypomere because it has an intimate relationship with, and is contributory to, the
| |
| development of the viscera. The somatic mesoderm, on the other hand, is the
| |
| mesoderm of the lateral or body-wall portion of the hypomere. The word
| |
| splanchnopleure is a noun and it designates the composite tissue of primitive
| |
| entoderm and splanchnic mesoderm, while the word somatopleure is applied
| |
| to the compound tissue formed by the primitive lateral wall of the hypomere
| |
| (somatic mesoderm) plus the primitive ectoderm overlying it. The coelom
| |
| proper or spianchnocoel is the space or cavity which lies between the splanchnic
| |
| and somatic layers of the lateral plate or hypomeric mesoderm. During later
| |
| development, it is the cavity in which the entrails lie.
| |
|
| |
| 3) Contributions of the Hypomere (Lateral Plate Mesoderm) to the External (Ectodermal or Epidermal) Body Tube. The somatopleural mesoderm
| |
| gives origin to a mass of cellular material which migrates outward to lie along
| |
| the inner aspect of the epidermal tube in the lateral and ventral portions of
| |
| the developing body (fig. 252A, D). In the dorsal and dorso-lateral regions of
| |
| the body, contributions from the sclerotome and dermatome apparently aid
| |
| in forming this tissue layer. The layer immediately below the epidermis constitutes the embryonic rudiment of the dermis. (See Chap. 12.)
| |
|
| |
| 4) Contributions of the Hypomere or Lateral Plate Mesoderm to the Dorsal
| |
| Body Areas. Many cells are given off both from splanchnic and somatic layers
| |
| of the hypomeric mesoderm to the dorsal body areas above and along either
| |
| side of the dorsal aorta (fig. 254), contributing to the mesenchymal “packing tissue†in the area between the notochord and differentiating somite, extending outward to the dermis.
| |
|
| |
| 5) Contributions of the Lateral Plate Mesoderm to the Walls of the Coelomic Cavities. The pericardial, pleural, and peritoneal cavities are lined, as
| |
| stated above, by an epithelial type of tissue called mesothelium (fig. 254A-E).
| |
| These coelomic spaces (see Chap. 20) are derived from the fusion of the
| |
| two primitive splanchnocoels or cavities of the two hypomeres. External to
| |
| the mesothelial lining of the coelomic spaces, there ultimately is developed a
| |
| fibrous, connective tissue layer. Thus, mesothelium and connective tissue form.
| |
|
| |
|
| |
|
| |
|
| |
| Fig. 255. This figure illustrates different types of body form in various vertebrates
| |
| during embryonic development. A, D, H, M, and Q show primitive embryonic body
| |
| form in the developing shark, rock fish, frog, chick, and human. B, larval form of
| |
| shark; E and F, larval forms of rock fish; I and J, larval forms of frog; N and O, larval
| |
| forms of chick; R, larval form of human. C, G, K, L, P, and S represent definitive
| |
| body form in the above species. (Figures on rockfish development (Roccus saxatilis) redrawn from Pearson: 1938, Bull. Bureau of Fisheries, L). S. Dept, of Commerce, vol.
| |
| 49; figures on chick redrawn from Hamburger and Hamilton: 1951, J. Morphol., vol.
| |
| 88; figure Q, of developing human embryo, redrawn and modified from model based
| |
| upon Normentafeln of Keibel and Elze: 1908, vol. 8, G. Fischer, Jena; Dimensions of
| |
| human embryos in R and S, from Mall: Chap. 8, vol. 1, Human Embryology, by
| |
| F. Keibel and F. P. Mall, 1910, Lippincott, Philadelphia.)
| |
|
| |
|
| |
| 531
| |
|
| |
|
| |
|
| |
| 532
| |
|
| |
|
| |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
|
| |
|
| |
| in general, the walls of the coelomic spaces. These two tissues arise directly
| |
| from the hypomeric mesoderm.
| |
|
| |
|
| 5. Embryonic Mesenchyme and Its Derivatives | | 5. Embryonic Mesenchyme and Its Derivatives |
|
| |
|
| The mesenchymal cells given off from the mesodermal tubes of the trunk
| |
| area, namely, (1) sclerotomic mesenchyme, (2) dermatomic mesenchyme,
| |
| (3) mesenchymal contributions from the lateral plate mesoblast (hypomere)
| |
| to the gut, skin, heart, and (4) the mesenchyme contributed to the general
| |
| regions of the body lying between the epidermal tube, coelom, notochord,
| |
| and neural tube, form, together with the head and tail mesoderm, the general
| |
| packing tissue which lies between and surrounding the internal tubular structures of the embryo (fig. 254). Its cells may at times assume polymorphous
| |
| or stellate shapes. This loose packing tissue of the embryo constitutes the
| |
| embryonic mesenchyme. (See Chap. 15.)
| |
|
| |
| This mesenchyme ultimately will contribute to the following structures of
| |
| the body:
| |
|
| |
| (a) Myocardium (cardiac musculature, etc.) and the epicardium or covering coelomic layer of the heart (Chap. 17),
| |
|
| |
| (b) endothelium of blood vessels, blood cells (Chap. 17),
| |
|
| |
| (c) smooth musculature and connective tissues of blood vessels (Chaps.
| |
| 16 and 17),
| |
|
| |
| (d) spleen, lymph glands, and lymph vessels (Chap. 17),
| |
|
| |
| (e) connective tissues of voluntary and involuntary muscles (Chap. 16),
| |
|
| |
| (f) connective tissues of soft organs, exclusive of the nerve system (Chap.
| |
| 15),
| |
|
| |
| (g) connective tissues in general, including bones and cartilage (Chap. 15),
| |
|
| |
| (h) smooth musculature of the gut tissues and gut derivatives (Chap. 16),
| |
|
| |
| (i) voluntary or striated muscles of the tail from tail-bud mesenchyme
| |
| (Chap. 16),
| |
|
| |
| (j) striated (voluntary) musculature of face, jaws, and throat, derived
| |
| from the lateral plate mesoderm in the anterior pharyngeal region
| |
| (Chap. 16),
| |
|
| |
| (k) striated (voluntary) extrinsic musculature of the eye (Chap. 16),
| |
|
| |
| (l) intrinsic, smooth musculature of the eye (Chap. 16),
| |
|
| |
| (m) tongue and musculature of bilateral appendages, derived from somitic
| |
| muscle buds (sharks) or from mesenchyme possibly of somitic origin
| |
| (higher vertebrates) (Chap. 16), and
| |
|
| |
| (n) chromatophores or pigment cells of the body from neural crest mesenchyme (Chap. 12).
| |
|
| |
|
| |
|
| |
| SUMMARY OF DERIVATIVES OF ORGAN-FORMING AREAS
| |
|
| |
|
| |
| 533
| |
|
| |
|
| |
| £. Summary of Later Derivatives of the Major Presumptive Organforming Areas of the Late Blastula and Gastrula
| |
|
| |
|
| 1. Neural Plate Area (Ectoderm) | | 1. Neural Plate Area (Ectoderm) |
|
| |
| This area gives origin to the following:
| |
|
| |
| (a) Neural tube,
| |
|
| |
| (b) optic nerves and retinae of eyes,
| |
|
| |
| (c) peripheral nerves and ganglia,
| |
|
| |
| (d) chromatophores and chromaffin tissue (i.e., various pigment cells of
| |
| the skin, peritoneal cavity, etc., chromaffin cells of supra-renal gland),
| |
|
| |
| (e) mesenchyme of the head, neuroglia, and
| |
|
| |
| (f) smooth muscles of iris.
| |
|
| |
|
| 2. Epidermal Area (Ectoderm) | | 2. Epidermal Area (Ectoderm) |
|
| |
|
| This area gives origin to:
| | 3. Entodermal Area |
| | |
| (a) Epidermal tube and derived structures, such as scales, hair, nails,
| |
| feathers, claws, etc.,
| |
| | |
| (b) lens of the eye, inner ear vesicles, olfactory sense area, general, cutaneous, sense organs of the peripheral area of the body,
| |
| | |
| (c) stomodaeum and its derivatives, oral cavity, anterior lobe of pituitary,
| |
| enamel organs, and oral glands, and
| |
| | |
| (d) proctodaeum from which arises the lining tissue of the anal canal.
| |
| | |
| 3. Entoderm AL Area | |
| | |
| From this area the following arise:
| |
| | |
| (a) Epithelial lining of the primitive gut tube or metenteron, including:
| |
| (1) epithelium of pharynx; epithelium pharyngeal pouches and their
| |
| derivatives, such as auditory tube, middle-ear cavity, parathyroids, and
| |
| thymus; (2) epithelium of thyroid gland; (3) epithelial lining tissue
| |
| of larynx, trachea, and lungs, and (4) epithelium of gut tube and gut
| |
| glands, including liver and pancreas,
| |
| | |
| (b) most of the lining tissue of the urinary bladder, vagina, urethra, and
| |
| associated glands,
| |
| | |
| (c) Seessel’s pocket or head gut, and
| |
| | |
| (d) tail gut.
| |
|
| |
|
| 4. Notochordal Area | | 4. Notochordal Area |
|
| |
| This area:
| |
|
| |
| (a) Forms primitive antero-posterior skeletal axis of all chordate forms,
| |
|
| |
| (b) aids in induction of central nerve tube.
| |
|
| |
|
| |
|
| |
| 534
| |
|
| |
|
| |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
|
| |
|
| |
| (c) gives origin to adult notochord of Amphioxus and cyclostomatous fishes
| |
| and to notochordal portions of adult vertebral column of gnathostomous
| |
| fishes and water-living amphibia, and
| |
|
| |
| (d) also, comprises the remains of the notochord in land vertebrates, such
| |
| as “nucleus pulposus†in man.
| |
|
| |
|
| 5. Mesodermal Areas | | 5. Mesodermal Areas |
|
| |
| These areas give origin to:
| |
|
| |
| (a) Epimeric, mesomeric, and hypomeric areas of primitive mesodermal
| |
| tube,
| |
|
| |
| (b) epimeric portion also aids in induction of central nerve tube,
| |
|
| |
| (c) muscle tissue, involuntary and voluntary,
| |
|
| |
| (d) mesenchyme, connective tissues, including bone, cartilage,
| |
|
| |
| (e) blood and lymphoid tissue,
| |
|
| |
| (f) gonads with exception of germ cells, genital ducts, and glandular tissues of male and female reproductive ducts, and
| |
|
| |
| (g) kidney, ureter, musculature and connective tissues of the bladder,
| |
| uterus, vagina, and urethra.
| |
|
| |
|
| 6. Germ-cell Area | | 6. Germ-cell Area |
|
| |
| This area gives origin to:
| |
|
| |
| (a) Primordial germ cells and probably to definitive germ cells of all vertebrates below mammals and
| |
|
| |
| (b) primordial germ cells of mammals and possibly to definitive germ cells.
| |
|
| |
|
| F. Metamerism | | F. Metamerism |
|
| |
| 1. Fundamental Metameric Character of the Trunk and
| |
| Tail Regions of the Vertebrate Body
| |
|
| |
| Many animals, invertebrate as well as vertebrate, are characterized by the
| |
| fact that their bodies are constructed of a longitudinal series of similar parts
| |
| or metameres. As each metamere arises during development in a similar
| |
| manner and from similar rudiments along the longitudinal or antero-posterior
| |
| axis of the embryo, each metamere is homologous with each of the other
| |
| metameres. This type of homology in which the homologous parts are arranged serially is known as serial homology. Metamerism is a characteristic
| |
| feature of the primitive and later bodies of arthropods, annelids, cephalochordates, and vertebrates.
| |
|
| |
| In the vertebrate group, the mesoderm of the trunk and tail exhibits a type
| |
| of segmentation, particularly in the epimeric or somitic area. Each pair of
| |
| somites, for example, denotes a primitive body segment. The nervous system
| |
|
| |
|
| |
|
|
| |
|
| |
|
| |
| ^OPTIC VESICLE
| |
| LENS PLACODE .
| |
|
| |
| ^ nasal placode
| |
| — —maxillary
| |
| process
| |
|
| |
| mandibular arch
| |
|
| |
|
| |
| branchial arch
| |
|
| |
|
| |
|
| |
|
| |
|
| |
| nasal placode
| |
|
| |
|
| |
| ORAL OPENING
| |
|
| |
| Laxillary PROCESstl^
| |
|
| |
| .
| |
|
| |
|
| |
|
| |
| mandibular ARCH
| |
|
| |
|
| |
| \ ^nasolateral
| |
| PROCESS
| |
|
| |
|
| |
| ^ NaSOMEDIAL -*
| |
|
| |
| process I
| |
| ''naso-optic furrow
| |
| 'maxillary process
| |
| "mandibular arch
| |
|
| |
|
| |
| hyomandibular cleft
| |
|
| |
|
| |
| NASOMEDIAL
| |
|
| |
| process
| |
|
| |
|
| |
| NASOLATERAL
| |
|
| |
| process
| |
|
| |
|
| |
| naso-optic
| |
|
| |
| furrow
| |
|
| |
|
| |
| 'hyomandibular
| |
|
| |
| CLEFT
| |
|
| |
|
| |
|
| |
|
| |
|
| |
| tubercles around
| |
| ^ hyomandibular CLEFT
| |
| § fusing to form
| |
|
| |
| f external EAR'
| |
|
| |
|
| |
|
| |
| ...»
| |
|
| |
|
| |
| NASOLATERAL PROCESS^
| |
|
| |
| NASOMEDIAL PROCESSES
| |
|
| |
| fusing to form PHILTRUM-.
| |
| OF LIP
| |
|
| |
| EXTERNAL EAR
| |
|
| |
| ear tubercles around
| |
| hyomandibular cleft
| |
|
| |
| -hyoid bone REGlONr
| |
|
| |
|
| |
| ih j 1
| |
|
| |
|
| |
|
| |
| F.O. 256. Developmental features of the human fac. Modified slightly from models by
| |
| B. Ziegler, Freiburg, after Karl Peter.
| |
|
| |
|
| |
| 535
| |
|
| |
|
| |
|
| |
| 536
| |
|
| |
|
| |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
|
| |
|
| |
| also manifests various degrees of segmentation (Chap. 19), although the
| |
| origin and arrangement of the peripheral nerves in the form of pairs, each
| |
| pair innervating a pair of myotomic derivatives of the somites, is the most
| |
| constant feature.
| |
|
| |
| In the cephalochordate, Amphioxus, the segmentation of the early mesoderm is more pronounced than that of the vertebrate group. As observed in
| |
| Chapter 10, each pair of somites is distinct and entirely separate from other
| |
| somitic pairs, and each pair represents all the mesoderm in the segment or
| |
| metamere. That is, all the mesoderm is segmented in Amphioxus. However,
| |
| in the vertebrate group, only the more dorsally situated mesoderm undergoes
| |
| segmentation, the hypomeric portion remaining unsegmented.
| |
|
| |
| 2. Metamerism and the Basic Morphology of the
| |
| Vertebrate Head
| |
|
| |
| While the primitive, metameric (segmental) nature of the vertebrate trunk
| |
| and tail areas cannot be gainsaid, the fundamental metamerism of the vertebrate head has been questioned. Probably the oldest theory supporting a
| |
| concept of cephalic segmentation was the vertebral theory of the skull, propounded by Goethe, Oken, and Owen. This theory maintained that the basic
| |
| structure of the skull demonstrated that it was composed of a number of
| |
| modified vertebrae, the occipital area denoting one vertebra, the basisphenoidtemporo-parietal area signifying another, the presphenoid-orbitosphenoidfrontal area denoting a third vertebra, and the nasal region representing a
| |
| fourth cranial vertebra. (Consult Owen, 1848.) This theory, as a serious
| |
| consideration of vertebrate head morphology was demolished by the classic
| |
| Croonian lecture given in 1858 by Huxley (1858) before the Royal Society
| |
| of London. His most pointed argument against the theory rested upon the
| |
| fact that embryological development failed to support the hypothesis that the
| |
| bones of the cranium were formed from vertebral elements.
| |
|
| |
| A factor which aroused a renewal of interest in a segmental interpretation
| |
| of the vertebrate head was the observation by Balfour (1878) that the head
| |
| of the elasmobranch fish, Scy Ilium, contained several pairs of pre-otic (prootic) somites (that is, somites in front of the otic or ear region). Since Balfour’s
| |
| publication, a large number of studies and dissertations have appeared in an
| |
| endeavor to substantiate the theory of head segmentation. The anterior portion of the central nervous system, cranial nerves, somites, branchial (visceral)
| |
| arches and pouches, have all served either singly or in combination as proffered
| |
| evidence in favor of an interpretation of the primitive segmental nature of
| |
| the head region. However, it is upon the head somites that evidence for a
| |
| cephalic segmentation mainly depends.
| |
|
| |
| A second factor which stimulated discussion relative to head segmentation
| |
| was the work of Locy (1895) who emphasized the importance of so-called
| |
| neural segments or neuromcres (Chap. 19) as a means of determining the
| |
|
| |
|
| |
|
| |
|
| |
|
| |
| ARROWS SHOW water CURRENTS
| |
|
| |
|
| |
| Fig. 257. Drawings of early frog tadpoles showing development of early systems.
| |
| (A) Frog tadpole (R. pipiens) of about 6 7 mm. It is difficult to determine the exact
| |
| number of vitelline arteries at this stage of development and the number given in the
| |
| figure is a diagrammatic representation. {A') Shows right and left ventral aortal divisions of bulbus cordis. (B) Anatomy of frog tadpole of about 10-18 mm. See also
| |
| figures 280 and 335.
| |
|
| |
|
| |
| 537
| |
|
| |
|
| |
|
| |
|
| |
|
| |
|
| |
| 540
| |
|
| |
|
| |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
|
| |
|
| |
| primitive segmental structure of the vertebrate brain. It is to be observed that
| |
| the more conservative figure 253, taken from Goodrich, does not emphasize
| |
| neuromeres, for, as observed by Kingsbury (’26, p. 85), the evidence is overwhelmingly against such an interpretation. The association of the cranial nerves
| |
| with the gill (branchial) region and the head somites, shown in figure 253,
| |
| will be discussed further in Chapter 19.
| |
|
| |
| A third factor which awakened curiosity, concerning the segmental theory
| |
| of head development, is branchiomerism. The latter term is applied to the
| |
| development of a series of homologous structures, segmentally arranged, in
| |
| the branchial region; these structures are the visceral arches and branchial
| |
| pouches referred to above. As mentioned there, the branchial pouches or outpocketings of the entoderm interrupt a non-segmented mass of lateral plate
| |
| (hypomeric) mesoderm, and this mesoderm secondarily becomes segmented
| |
| and located within the visceral arches. These arches when formed, other than
| |
| possibly the mandibular and the hyoid arches (fig. 253), do not correspond
| |
| with the dorsal somitic series. Consequently, “branchiomerism does not, therefore, coincide with somitic metamerism.†(See Kingsbury, ’26, p. 106.)
| |
|
| |
| Undoubtedly, much so-called “evidence†has been accumulated to support
| |
| a theory of head segmentation. A considerable portion of this evidence apparently is concerned more with segmentation as an end in itself than with a
| |
| frank appraisal of actual developmental conditions present in the head (Kingsbury and Adelmann, ’24 and Kingsbury, ’26). However, the evidence which
| |
| does resist critical scrutiny is the presence of the head somites which includes
| |
| the pre-otic somites and the first three or four post-otic somites. While the
| |
| pre-otic somites are somewhat blurred and slurred over in their development
| |
| in many higher vertebrates, the fact of their presence in elasmobranch fishes
| |
| is indisputable and consistent with a conception of primitive head segmentation.
| |
|
| |
| Furthermore, aside from a possible relationship with head-segmentation
| |
| phenomena, the appearance of the pre-otic and post-otic head somites coincides with basic developmental tendencies. As observed above, for example,
| |
| there is a tendency for nature to use generalized developmental procedures in
| |
| the early development of large groups of animals (see von Baer’s laws, p. 522,
| |
| and also discussion relative to Haeckel’s biogenetic law in Chap. 7). Nature,
| |
| in other words, is utilitarian, and one can be quite certain that if general
| |
| developmental procedures are used, they will prove most efficient when all
| |
| factors are considered. At the same time, while generalized procedures may
| |
| be used, nature does not hesitate to mar or elide parts of procedures when
| |
| needed to serve a particular end. The obliteration of developmental steps
| |
| during development is shown in the early development of the mesoderm in
| |
| the vertebrate group compared to that which occurs in Amphioxus. In the
| |
| vertebrate embryo, as observed previously, the hypomeric mesoderm is unsegmented except in a secondary way and in a restricted area as occurs in
| |
| branchiomerism. However, in Amphioxus, early segmentation of the meso
| |
|
| |
|
| |
| METAMERISM
| |
|
| |
|
| |
| 541
| |
|
| |
|
| |
| derm is complete dorso-ventrally, including the hypomeric region of the
| |
| mesoderm. It becomes evident, therefore, that the suppression of segmentation
| |
| in the hypomeric area in the vertebrate embryo achieves a precocious result
| |
| which the embryo of Amphioxus reaches only at a later period of development. Presumably in the vertebrate embryo, segmentation of the epimeric
| |
| mesoderm is retained because it serves a definite end, whereas segmentation
| |
| of the hypomeric mesoderm is deleted because it also leads to a necessary end
| |
| result in a direct manner.
| |
|
| |
| When applied to the developing head region, this procedure principle means
| |
| this: A primitive type of segmentation does tend to appear in the pre-otic
| |
| area as well as in the post-otic portion of the head, as indicated by the pre-otic
| |
| and post-otic somites, and secondarily there is developed a branchial metam
| |
|
| |
| GASSERIAN GANGLION I
| |
| ME TENCEPHAUON
| |
|
| |
| geniculate GANGLION OF NERVE Stt
| |
| ACOUSTIC GANGLION OF NERVE :
| |
|
| |
| MYf lencephalon
| |
| OTIC VESICLE
| |
|
| |
| SUPERIOR GANGLION OF NERVE H
| |
| JUGULAR GANGLION OF NERVE X
| |
| PETROSAL GANGLION OF NERVE IX ^
| |
|
| |
| NERVE :
| |
|
| |
| NOOOSE ganglion OF nerve::
| |
|
| |
| NERVE
| |
|
| |
| SPINAL CORO-^
| |
|
| |
| pharyngeal pouch in-<:
| |
| pharyngeal POUCHBC;
| |
| thyroid BODY
| |
| BUL0US COROIS
| |
|
| |
|
| |
| MESENCEPHALON
| |
|
| |
|
| |
| â– NERVE 33
| |
|
| |
| NERVE m
| |
|
| |
| infundibulum
| |
| E’S POCKET
| |
| SEESSEL'S POCKET
| |
| CHOROID FISSURE
| |
| OlENCEPHALON
| |
|
| |
|
| |
|
| |
| DORSAL aorta
| |
| NOTOCHORD
| |
| stomach
| |
| LIVER
| |
|
| |
|
| |
| ventral pancreasdorsal pancreas
| |
| gall blaode
| |
| MESONEPHROS- —
| |
|
| |
|
| |
| MIDGUT
| |
| AN DUCT
| |
|
| |
| glomeruli
| |
|
| |
| COLLECTING DUCT
| |
| HINDGUT
| |
|
| |
| SPINAL GANGLION
| |
|
| |
|
| |
| Fig. 259. Chick embryo reconstruction of about 100 hrs. of incubation with special
| |
| reference to the nervous and urinary systems. See also fig. 336D.
| |
|
| |
|
| |
|
| |
|
| |
| bation. Reference should
| |
| 5
| |
|
| |
|
| |
| BASIC HOMOLOGY OF ORGAN SYSTEMS
| |
|
| |
|
| |
| 545
| |
|
| |
|
| |
| erism (branchiomerism) . However, all these segmental structures serve a
| |
| definite end. In other areas, head development proceeds in a manner which
| |
| obscures segmentation, for the probable reason that segmentation does not fit
| |
| into the developmental pattern which must proceed directly and precociously
| |
| to gain a specific end dictated by problems peculiar to head development.
| |
|
| |
| {Note: For a critical analysis of the supposed facts in favor of segmentation,
| |
| together with a marshaling of evidence against such an interpretation, consult
| |
| Kingsbury and Adelmann (’24) and for a favorable interpretation of the segmental nature of the head region, see Goodrich (’18) and Delsman (’22).
| |
| Figure 253 is taken from Goodrich (’18), and the various structures which
| |
| favor a segmental interpretation of the head region are shown.)
| |
|
| |
|
| G. Basic Homology of the Vertebrate Organ Systems | | G. Basic Homology of the Vertebrate Organ Systems |
Line 1,310: |
Line 642: |
| 1. Definition | | 1. Definition |
|
| |
|
| Homology is the relationship of agreement between the structural parts of
| | 2. Basic Homology of Vertebrate Blastulae, Gastrulae, and Tubulated Embryos |
| one organism and the structural parts of another organism. An agreeable
| |
| relationship between two structures is established if:
| |
| | |
| ( 1 ) the two parts occupy the same relative position in the body,
| |
| | |
| (2) they arise in the same way embryonically and from the same rudiments, and
| |
| | |
| (3) they have the same basic potencies.
| |
| | |
| By basic potency is meant the potency which governs the initial and fundamental development of the part; it should not be construed to mean the
| |
| ability to produce the entire structure. To the basic potency, other less basic
| |
| potencies and modifying factors may be added to produce the adult form of
| |
| the structure.
| |
| | |
| 2. Basic Homology of Vertebrate Blastulae, Gastrulae, and | |
| Tubulated Embryos | |
| | |
| In Chapters 6 and 7, the basic conditions of the vertebrate blastula were
| |
| surveyed, and it was observed that the formative portion of all vertebrate
| |
| blastulae presents a basic pattern, composed of major presumptive organforming areas oriented around the notochordal area and a blastocoelic space.
| |
| During gastrulation (Chap. 9), these areas are reoriented to form the basic
| |
| pattern of the gastrula, and although round and flattened gastrulae exist, these
| |
| form one, generalized, basic pattern, composed of three germ layers arranged
| |
| around the central axis or primitive notochordal rod. Similarly, in Chapter
| |
| 10, the major organ-forming areas are tubulated to form an elongated embryo,
| |
| composed of head, pharyngeal, trunk, and tail regions. As tubulation is effected in much the same manner throughout the vertebrate series and as the
| |
| pre-chordal plate mesoderm, foregut entoderm, notochord, and somitic meso
| |
| | |
| | |
| 546
| |
| | |
| | |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
| | |
| | |
| geniculate ganglion of seventh nerve
| |
| | |
| ACOUSTIC GANGLION OF EIGHTH NERVE
| |
| AUDITORY VESICLE
| |
| | |
| | |
| JU^dLAR GANGLION
| |
| | |
| SUPERIOR GANGLION
| |
| NINTH NERV
| |
| ACCESSORY ganglion
| |
| BASILAR ARTERY
| |
| DORSAL ROOT
| |
| GANGLION OP FIRST
| |
| | |
| cervical nerve
| |
| aortal arch I
| |
| | |
| AORTAL ARCH II
| |
| AORTAL ARCH III
| |
| AORTAL ARCH IV
| |
| AORTAL ARCH VT
| |
| PULMONARY ARTERY
| |
| TRACHEA
| |
| NOTOCHORD
| |
| RIGHT ATRIUM
| |
| LUNG
| |
| | |
| | |
| | |
| SMALL
| |
| | |
| INTESTINE
| |
| | |
| hepatic
| |
| | |
| PORTAL VEIN
| |
| DORSAL AORTA
| |
| | |
| | |
| OMPHALOMESENTERIC
| |
| ARTERY
| |
| | |
| (FUTURE SUPERIOR
| |
| MESENTERIC ARTERY)
| |
| | |
| | |
| GLOMERULUS
| |
| MESONEPHRIC TUBULE
| |
| | |
| | |
| DORSAL AORTA
| |
| MESONEPHRIC DUCT
| |
| | |
| | |
| Fig. 261. Drawings of pig embryos of about 9.5 to 12 mm. (A) Reconstruction of about
| |
| 9.5 to 10 mm. pig embryo with special emphasis on the arterial system.
| |
| | |
| derm appear to be the main organizing influence throughout the series (Chap.
| |
| 10), the conclusion is inescapable that the tubulated embryos of all vertebrates
| |
| are homologous basically, having the same relative parts, arising in the same
| |
| manner, and possessing the same basic potencies within the parts. To this
| |
| conclusion must be added a caution, namely, that, although the main segments
| |
| or specific organ regions along each body tube of one species are homologous
| |
| with similar segments along corresponding tubes of other species, variations
| |
| may exist and non-homologous areas may be insinuated or homologous areas
| |
| | |
| | |
| | |
| BASIC HOMOLOGY OF ORGAN SYSTEMS
| |
| | |
| | |
| 547
| |
| | |
| | |
| may be deleted along the respective tubes. Regardless of this possibility, a
| |
| basic homology, however, appears to exist.
| |
| | |
| During later development through larval and definitive body-form stages,
| |
| a considerable amount of molding or plasis by environmental and intrinsic
| |
| factors may occur. An example of plasis is given in the development of the
| |
| forelimb rudiment of the fish, frog, bird, and pig. In the definitive form, these
| |
| structures assume different appearances and are adapted for different func
| |
| | |
| METENCEPHALON
| |
| | |
| | |
| BASILAR ARTERY
| |
| NOTOCHORD
| |
| | |
| ROOT OF TONGUE
| |
| THYROID GLAND
| |
| developing epiglottis
| |
| AORTIC ARCH III
| |
| L ARYN X
| |
| | |
| | |
| ESOPH AGU S
| |
| VALVES OF
| |
| | |
| SINUS 'VENOSUS/
| |
| LUNG bud'
| |
| | |
| SPINAL CORD
| |
| SINUS VENOSU;
| |
| | |
| | |
| GALL BLADDER
| |
| | |
| NOTOCHORDOORSAL AORTA
| |
| | |
| DEVELOPING
| |
| VERTEBRAE
| |
| | |
| MESONEPHRIC
| |
| KIDNE
| |
| | |
| | |
| | |
| MESENCEPHALON
| |
| | |
| | |
| TUBERCULUM
| |
| | |
| ju / POSTERIUS
| |
| ~ — ^INFUNDIBULUM
| |
| OIEUCEPHALON
| |
| | |
| rathke's pocket
| |
| | |
| SEESSEL'S POCKET
| |
| — -OPTIC CHIASMA
| |
| | |
| -RECESSUS OPTICUS
| |
| TELENCEPHALON
| |
| AMINA TERMINALIS
| |
| TONGUE
| |
| BULBUS CORDIS
| |
| | |
| | |
| EXTRA-EMBRYONIC COELOM
| |
| UMBILICAL CORD
| |
| | |
| | |
| ALLANTOIC DIVERTICULUM
| |
| GENITAL EMINENCE
| |
| PROCTODAEUM
| |
| | |
| CLOACA
| |
| | |
| | |
| ALLANTOIC STALK
| |
| | |
| | |
| B.
| |
| | |
| | |
| metanephrogenous
| |
| | |
| TISSUE SPINAL GANGLION
| |
| | |
| | |
| Fig. 261 — (Continued} (B) Median sagittal section of 10 mm. embryo.
| |
| | |
| | |
| | |
| VEIN OF maxillary REGION
| |
| (BRANCH OF INTERNAL JUGULAR)
| |
| | |
| | |
| OTIC VESICLE
| |
| | |
| | |
| VEIN OF
| |
| | |
| MANDIBULAR REGION
| |
| BRANCH OF EXTERNAL
| |
| JUGULAR)
| |
| | |
| INTERNAL JUGULAR
| |
| VEIN
| |
| DORSAL
| |
| | |
| jSEGMENTAL VEINS
| |
| EXTERNAL
| |
| JUGULAR VEIN
| |
| | |
| | |
| | |
| LEFT DUCT OF CUVIER
| |
| RIGHT VITELLINE VEIN
| |
| LIVER
| |
| DUCTUS VENOSUS
| |
| HEPATIC VEINS
| |
| PORTAL VEIN
| |
| | |
| | |
| UMBILICAL
| |
| | |
| ARTERY
| |
| | |
| | |
| 'TRANSVERSE ANASTOMOSIS
| |
| OF SITBCAROINALS
| |
| | |
| | |
| POSTERIOR CARDINAL
| |
| VEIN
| |
| | |
| | |
| PIG EMBRYO SHOWING RIGHT HALF
| |
| OF VENOUS SYSTEM
| |
| | |
| | |
| Fig. 261 — (Continued) (C) Lateral view of 12 mm. embryo showing venous system.
| |
| (C is redrawn and modified from Minot; 1903, A Laboratory Text-book of Embryology,
| |
| Blakiston, Philadelphia.)
| |
| | |
| | |
| 548
| |
| | |
| | |
| | |
| | |
| Fig. 262. Sections and stereograms of 10 mm. pig embryo.
| |
| | |
| | |
| MCSCNCHYME^
| |
| | |
| | |
| | |
| Ibl— (Continued) Sections and stereograms of 10 mm. pig embryo
| |
| | |
| | |
| | |
| | |
| BIBLIOGRAPHY
| |
| | |
| | |
| 551
| |
| | |
| | |
| tional purposes. Basically, however, these structures are homologous, although
| |
| plasis produces adult forms which appear to be different.
| |
| | |
| A further statement should be added, concerning that type of molding or
| |
| plasis of a developing structure which produces similar structures from conditions which have had a different genetic history. For example, the bat’s fore
| |
| limb rudiment is molded to produce a structure resembling superficially that
| |
| of the bird, although modern bats and birds have arisen through different lines
| |
| of descent. Similarly, the teeth of certain teleost fishes superficially resemble
| |
| the teeth of certain mammals, an effect produced from widely diverging lines
| |
| of genetic descent. These molding effects or homoplasy, which produce superficially similar structures as a result of adaptations to certain environmental
| |
| conditions, are called convergence, parallelism, and analogy. An example of
| |
| experimental homoplasy is the induction of eye lenses in the embryo by the
| |
| transplantation of optic-cup material to a place in the epidermis which normally does not produce a lens.
| |
| | |
| {Note: For a discussion of homology, homogeny, plasis, convergence, etc.,
| |
| see Tait, ’28.)
| |
| | |
| | |
| Bibliography
| |
| | |
| | |
| Adelmann, H. B. 1925. The development
| |
| of the neural folds and cranial ganglia
| |
| of the rat. J. Comp. Neurol. 39:19.
| |
| | |
| . 1927. The development of the eye
| |
| | |
| muscles of the chick. J. Morphol. 44:29.
| |
| | |
| . 1932. The development of the
| |
| | |
| prechordal plate and mesoderm of Ambly stoma piinctatum. J. Morphol. 54:1.
| |
| | |
| Baer, K. E. von. 1828-1837. liber Entwickelungsgeschichte der Thiere. Beobachtung und Reflexion. Erster Theil,
| |
| 1828; Zweiter Theil, 1837. Konigsberg,
| |
| Borntriiger.
| |
| | |
| Balfour, F. M. 1878. Monograph on the
| |
| development of elasmobranch fishes. Republished in 1885 in The Works of
| |
| Francis Maitland Balfour, edited by M.
| |
| Foster and A. Sedgwick, vol. 1. The
| |
| Macmillan Co., London.
| |
| | |
| Delsman, H. C. 1922. The Ancestry of
| |
| Vertebrates. Valkoff & Co., Amersfoort,
| |
| Holland.
| |
| | |
| Goodrich, E. S. 1918. On the development
| |
| of the segments of the head of Scy Ilium.
| |
| Quart. J. Micr. Sc. 63:1.
| |
| | |
| Hill, J. P. and Tribe, M. 1924. The early
| |
| development of the cat {Felis dornestica).
| |
| Quart. J. Micr. Sc. 68:513.
| |
| | |
| | |
| Huxley, T. H. 1858. The Croonian lecture
| |
| — on the theory of the vertebrate skull.
| |
| Proc. Roy. Soc., London, s.B. 9:381.
| |
| | |
| Kingsbury, B. F. 1915. The development
| |
| of the human pharynx. 1. Pharyngeal
| |
| derivatives. Am. J. Anat. 18:329.
| |
| | |
| . 1924. The significance of the so
| |
| called law of cephalocaudal differential
| |
| growth. Anat. Rec, 27:305.
| |
| | |
| . 1926. Branchiomerism and the
| |
| | |
| theory of head segmentation. J. Morphol.
| |
| 42:83.
| |
| | |
| and Adelmann, H. B. 1924. The
| |
| | |
| morphological plan of the head. Quart.
| |
| J. Micr, Sc. 68:239.
| |
| | |
| Kyle, H. M. 1926. The Biology of Fishes.
| |
| Sidgwick and Jackson, Ltd., London.
| |
| | |
| Landacre, F. L. 1921. The fate of the
| |
| neural crest in the head of urodeles. J.
| |
| Comp. Neurol. 33:1.
| |
| | |
| Lewis, W. H. 1910. Chapter 12. The development of the muscular system in
| |
| Manual of Human Embryology, edited
| |
| by F. Keibel and F. P. Mall. J. B. Lippincott Co., Philadelphia.
| |
| | |
| Locy, W. A. 1895. Contribution to the
| |
| structure and development of the vertebrate head. J. Morphol. 11:497.
| |
| | |
| | |
| | |
| 552
| |
| | |
| | |
| BASIC FEATURES OF VERTEBRATE MORPHOGENESIS
| |
| | |
| | |
| Newth, D. R. 1951. Experiments on the
| |
| neural crest of the lamprey embryo. J.
| |
| Exper. Biol. 28:17.
| |
| | |
| Owen, R. 1848. On the archetype and
| |
| homologies of the vertebrate skeleton.
| |
| John Van Voorst, London.
| |
| | |
| Raven, C. P. 1933a. Zur Entwicklung der
| |
| Ganglienleiste. I. Die Kinematik der
| |
| Ganglienleistenentwicklung bei den Urodelen. Arch. f. Entwlngsmech. d. Organ.
| |
| 125:210.
| |
| | |
| . 1933b. Zur Entwicklung der Ganglienleiste. III. Die Induktionsfahigkeit
| |
| des Kopfganglienleistenmaterials von
| |
| Rana fusca.
| |
| | |
| | |
| Stone, L. S. 1922. Experiments on the development of the cranial ganglia and
| |
| the lateral line sense organs in Amblystoma pimctatum. J. Exper. Zool. 35:421.
| |
| | |
| . 1926. Further experiments on the
| |
| | |
| extirpation and transplantation of mesectoderm in Amhlystorna punctatum. J.
| |
| Exper. Zool. 44:95.
| |
| | |
| . 1929. Experiments showing the
| |
| | |
| role of migrating neural crest (mesectoderm) in the formation of head skeleton and loose connective tissue in Rana
| |
| paliistris. Arch. f. Entwicklngsmech. d.
| |
| Organ. 118:40.
| |
|
| |
|
| Tait, J. 1928. Homology, analogy and
| | ==Bibliography== |
| plasis. Quart. Rev. Biol. Ill: 151.
| |
Nelsen OE. Comparative embryology of the vertebrates (1953) Mcgraw-Hill Book Company, New York.
Historic Disclaimer - information about historic embryology pages
|
Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers)
|
Part III The Development of Primitive Embryonic Form
Part III - The Development of Primitive Embryonic Form: 6. Cleavage (Segmentation) and Blastulation | 7. The Chordate Blastula and Its Significance | 8. The Late Blastula in Relation to Certain Innate Physiological Conditions: Twinning | 9. Gastrulation | 10. Tubulation and Extension of the Major Organ-forming Areas: Development of Primitive Body Form | 11. Basic Features of Vertebrate Morphogenesis
The general procedures leading to the development of primitive embryonic body form
in the chordate group of animals are:
( 1 ) Cleavage. Cleavage is the division of the egg into progressively smaller cellular
units, the blaslomeres (Chap. 6).
(2) Blastulation. Blastulalion results in the formation of the blastula. The blastula
is composed of a cellular blastoderm in relation to a fluid-filled cavity, the blastocoel.
The blastoderm of the late blastula is composed of neural, epidermal, notochordal,
mesodermal, and entodermal major presumptive organ-forming areas. In the phylum
Chordata, the notochordal area is the central region around which the other areas are
oriented (Chap. 7). The major presumptive organ-forming areas of the late blastula
exist in various degrees of differentiation (Chap. 8).
(3) Gastrulation. This is the process which effects a reorientation of the presumptive
organ-forming areas and brings about their axiation antero-posteriorly in relation to the
notochordal axis and the future embryonic body (Chap. 9). During gastrulation the
major organ-forming areas are subdivided into minor areas or fields, each field being
restricted to the development of a particular organ or part. (Pp. 378, 446, 447.
(4) Following gastrulation, the next step in the development of embryonic body form
is tubulation and extension of the major organ-forming areas (Chap. 10).
(5) As tubulation and extension of the organ-forming areas is effected, the basic or
fundamental conditions of the future organ systems are established, resulting in the
development of primitive body form. As the development of various vertebrate embryos
is strikingly similar up to this point, the primitive embryonic body forms of all vertebrates
resemble each other (Chap. II).
In the drawings presented in Part III, the following scheme for designating the major
organ-forming areas existing within the three germ layers is adhered to:
Cleavage (Segmentation) and Blastulation
6. Cleavage (Segmentation) and Blastulation
A. General considerations
1. Definitions
2. Early history of the cleavage (cell-division) concept
3. Importance of the cleavage-blastular period of development
a. Morphological relationships of the blastula
b. Physiological relationships of the blastula
1 ) Hybrid crosses
2) Artificial parthenogenesis
3) Oxygen-block studies
4. Geometrical relations of early cleavage
a. Meridional plane
b. Vertical plane
c. Equatorial plane
d. Latitudinal plane
5. Some fundamental factors involved in the early cleavage of the egg
a. Mechanisms associated with mitosis or cell division
b. Influence of cytoplasmic substance and egg organization upon cleavage
1) Yolk
2) Organization of the egg
c. Influence of first cleavage amphiaster on polyspermy
d. Viscosity changes during cleavage
e. Cleavage laws
1 ) Sach’s rules
2) Hertwig’s laws
6. Relation of early cleavage planes to the antero-posterior axis of the embryo
B. Types of cleavage in the phylum Chordata
1. Typical holoblastic cleavage
a. Amphioxus
b. Frog (Rana pipiens and R. sylvatica)
c. Cyclostomata
2. Atypical types of holoblastic cleavage
a. Holoblastic cleavage in the egg of the metatherian and eutherian mammals
1 ) General considerations
2) Early development of the rabbit egg
a) Two-cell stage
b) Four-cell stage
c) Eight-cell stage
d) Sixteen-cell stage
e) Morula stage
f) Early blastocyst
3) Types of mammalian blastocysts (blastulae)
b. Holoblastic cleavage of the transitional or intermediate type
1) Amhystoma maculatum (punctatum)
2) Lepidosiren paradoxa
3) Necturus maculosus
4) Acipenser sturio
5) Amia calva
6) Lepisosteus (Lepidosteus) osseus
7) Gymnophionan amphibia
3. Meroblastic cleavage
a. Egg of the common fowl
1 ) Early cleavages
2) Formation of the periblast tissue
3) Morphological characteristics of the primary blastula
4) Polyspermy and fate of the accessory sperm nuclei
b. Elasmobranch fishes
1 ) Cleavage and formation of the early blastula
2) Problem of the periblast tissue in elasmobranch fishes
c. Teleost fishes
1) Cleavage and early blastula formation
2) Origin of the periblast tissue in teleost fishes
d. Prototherian Mammalia
e. Cleavage in the California hagfish, Polistotrema (Bdellostorna) stouti
C. What is the force which causes the blastomeres to adhere together during early
cleavage?
D. Progressive cytoplasmic inequality and nuclear equality of the cleavage blastomeres
1. Cytoplasmic inequality of the early blastomeres
2. Nuclear equality of the early blastomeres
E. Quantitative and qualitative cleavages and their influence upon later development
The Chordate Blastula and Its Significance
7. The Chordate Blastula and Its Significance
A. Introduction
1. Blastulae without auxiliary tissue
2. Blastulae with auxiliary or trophoblast tissue
3. Comparison of the two main blastular types
B. History of the concept of specific, organ-forming areas
C. Theory of epigenesis and the germ-layer concept of development
D. Introduction of the words ectoderm, mesoderm, endoderm
E. Importance of the blastular stage in Haeckel's theory of The Biogenetic Law of Embryonic Recapitulation
F. Importance of the blastular stage in embryonic development
G. Description of the various types of chordate blastulae with an outline of their organforming areas
1. Protochordate blastula
2. Amphibian blastula
3. Mature blastula in birds
4. Primary and secondary reptilian blastulae
5. Formation of the late mammalian blastocyst (blastula)
a. Prototherian mammal, Echidna
b. Metatherian mammal, Didelphys
c. Eutherian mammals
6. Blastulae of teleost and elasmobranch fishes
7. Blastulae of gymnophionan amphibia
Late Blastula in Relation to Certain Innate Physiological Conditions: Twinning
8. The Late Blastula in Relation to Certain Innate Physiological Conditions: Twinning
A. Introduction
B. Problem of differentiation
1. Definition of differentiation; kinds of differentiation
2. Self-differentiation and dependent differentiation
C. Concept of potency in relation to differentiation
1. Definition of potency
2. Some terms used to describe different states of potency
a. Totipotency and harmonious totipotency
b. Determination and potency limitation
c. Prospective potency and prospective fate
d. Autonomous potency
c. Competence
D. The blastula in relation to twinning
1. Some definitions
a. Dizygotic or fraternal twins
b. Monozygotic or identical twins
c. Polyembryony •
2. Basis of true or identical twinning
3. Some experimentally produced, twinning conditions
E. Importance of the organization center of the late blastula
Gastrulation
| 9. Gastrulation
A. Some definitions and concepts
1. Gastrulation
2. Primitive vertebrate body plan in relation to the process of gastrulation
a. Fundamental body plan of the vertebrate animal
b. The gastrula in relation to the primitive body plan
c. Chart of blastula, gastrula, and primitive, body-form relationships (fig. 188)
B. General processes involved in gastrulation
C. Morphogenetic movement of cells
1. Importance of cell movements during development and in gastrulation
2. Types of cell movement during gastrulation
a. Epiboly
b. Emboly
3. Description of the processes concerned with epiboly
4. Description of the processes involved in emboly
a. Involution and convergence
b. Invagination
c. Concrescence
d. Cell proliferation
e. Polyinvagination
f. Ingression
g. Delamination
h. Divergence
i. Extension
D. The organization center and its relation to the gastrulative process
1. The organization center and the primary organizer
2. Divisions of the primary organizer
E. Chemodifferentiation and the gastrulative process
F. Gastrulation in various Chordata
1. Amphioxus
a. Orientation
b. Gastrulative movements
1 ) Emboly
2) Epiboly
3) Antero-posterior extension of the gastrula and dorsal convergence of the
mesodermal cells
4) Closure of the blastopore
c. Resume of cell movements and processes involved in gastrulation of Amphioxus
1 ) Emboly
2) Epiboly
2. Gastrulation in Amphibia with particular reference to the frog
a. Introduction
1) Orientation
2) Physiological changes which occur in the presumptive, organ-forming areas
of the late blastula and early gastrula as gastrulation progresses
b. Gastrulation
1) Emboly
2) Epiboly
3) Embryo produced by the gastrulative processes
4) Position occupied by the pre -chordal plate material
c. Closure of the blastopore and formation of the neurenteric canal
d. Summary of morphogenetic movements of cells during gastrulation in the frog
and other Amphibia
1) Emboly
2) Epiboly
3. Gastrulation in reptiles
a. Orientation
b. Gastrulation
4. Gastrulation in the chick
a. Orientation
b. Gastrulative changes
1) Development of primitive streak as viewed from the surface of stained
blastoderms
2) Cell movements in the epiblast involved in primitive-streak formation as
indicated by carbon-particle marking and vital-staining experiments
3) Cell movements in the hypoblast and the importance of these movements
in primitive-streak formation
4) Primitive pit notochordal canal
5) Resume of morphogenetic movements of cells during gastrulation in the
chick
5. Gastrulation in mammals
a. Orientation
b. Gastrulation in the pig embryo
c. Gastrulation in other mammals
6. Gastrulation in teleost and elasmobranch fishes
a. Orientation
b. Gastrulation in teleost fishes
1) Emboly
2) Epiboly
3) Summary of the gastrulative processes in teleost fishes
a) Emboly
b) Epiboly
4) Developmental potencies of the germ ring of teleost fishes
c. Gastrulation in elasmobranch fishes
7. Intermediate types of gastrulative behavior
G. The late gastrula as a mosaic of specific, organ-forming territories
H. Autonomous theory of gastrulative movements
I. Exogastrulation
J. Pre-chordal plate and cephalic projection in various chordates
K. Blastoporal and primitive-streak comparisons
Development of Primitive Body Form
10. Tubulation and Extension of the Major Organ-forming Areas: Development of Primitive Body Form
A. Introduction
1. Some of the developmental problems faced by the embryo after gastrulation
a. Tabulation
b. Increase in size and antero-posteri(*)r extension of the tubulated, major organforming areas
c. Regional modifications of the tubulated areas
2. Common, vertebrate, embryonic body form
3. Starting point for tabulation
4. Developmental processes which accomplish tabulation
a. Immediate processes
b. Auxiliary processes
5. Blastocoelic space and body-form development
6. Primitive circulatory tubes or blood vessels
7. Extra-embryonic membranes
B. Tabulation of the neural, epidermal, entodermal, and mesodermal, organ-forming
areas in the vertebrate group
1. Neuralization or the tabulation of the neural plate area
a. Definition
b. Neuralizative processes in the Vertebrata
1) Thickened keel method
2) Neural fold method
c. Closure of the blastopore in rounded gastrulae, such as that of the frog
d. Anterior and posterior neuropores; neurenteric canal
2. Epidermal tabulation
a. Development of the epidermal tube in Amphibia
b. Tabulation of the epidermal area in flat blastoderms
3. Formation of the primitive gut tube (enteric tabulation)
a. Regions of primitive gut tube or early metenteron
b. Formation of the primitive metenteron in the frog
c. Formation of the tubular metenteron in flat blastoderms
4. Tabulation (coelom formation) and other features involved in the early differentiation of the mesodermal areas
a. Early changes in the mesodermal areas
1) Epimere; formation of the somites
2) Mesomere
3) Hypomere
b. Tabulation of the mesodermal areas
C. Notochordal area
D. Lateral constrictive movements
E. Tubulation of the neural, epidermal, entodermal, and mesodermal, organ-forming
areas in Amphioxus
1. Comparison of the problems of tubulation in the embryo of Amphioxus with that
of the embryos in the subphylum Vertebrata
a. End-bud growth
b. Position occupied by the notochord and mesoderm at the end of gastrulation
2. Neuralization and the closure of the blastopore
3. Epidermal tubulation
4. Tubulation of the entodermal area
a. Segregation of the entoderm from the chordamesoderm and the formation of
the primitive metenteric tube
b. Formation of the mouth, anus, and other specialized structures of the metenteron
5. Tubulation of the mesoderm
6. Later differentiation of the myotomic (dorsal) area of the somite
7. Notochord
F. Early development of the rudiments of vertebrate paired appendages
G. The limb bud as an illustration of the field concept of development in relation to the
gastrula and the tubulated embryo
H. Cephalic flexion and general body bending and rotation in vertebrate embryos
I. Influences which play a part in tubulation and organization of body form
J. Basic similarity of body-form development in the vertebrate group of chordate animals
Basic Features of Vertebrate Morphogenesis
11. Basic Features of Vertebrate Morphogenesis
A. Introduction
1. Purpose of This Chapter
2. Definitions
a. Morphogenesis and Related Terms
b. Primitive, Larval, and Definitive Body Forms (see fig. 255)
1) Primitive Body Form.
2) Larval Body Form.
3) Definitive Body Form.
3. Basic or Fundamental Tissues
B. Transformation of the Primitive Body Tubes into the Fundamental
or Basic Condition of the Various Organ Systems
Present in the Primitive Embryonic Body
1. Processes Involved in Basic System Formation
(a) extension and growth of the body tubes,
(b) saccular outgrowths (evaginations) and ingrowths (invaginations)
from restricted areas of the tubes,
(c) cellular migrations away from the primitive tubes fo other tubes and
to the spaces between the tubes, and
(d) unequal growth of different areas along the tubes.
2. Fundamental Similarity of Early Organ Systems
C. Laws of von Baer
D. Contributions of the Mesoderm to Primitive Body Formation and
Later Development
1. Types of Mesodermal Cells
2. Origin of the Mesoderm of the Head Region
a. Head Mesoderm Derived from the Anterior Region of the Trunk
b. Head Mesoderm Derived from the Pre-chordal Plate
c. Head Mesoderm Contributed by Neural Crest Material
d. Head Mesoderm Originating from Post-otic Somites
3. Origin of the Mesoderm of the Tail
4. Contributions of the Trunk Mesoderm to the Developing Body
a. Early Differentiation of the Somites or Epimere
b. Early Differentiation of the Mesomere (Nephrotome)
c. Early Differentiation and Derivatives of the Hypomere
5. Embryonic Mesenchyme and Its Derivatives
1. Neural Plate Area (Ectoderm)
2. Epidermal Area (Ectoderm)
3. Entodermal Area
4. Notochordal Area
5. Mesodermal Areas
6. Germ-cell Area
F. Metamerism
G. Basic Homology of the Vertebrate Organ Systems
1. Definition
2. Basic Homology of Vertebrate Blastulae, Gastrulae, and Tubulated Embryos
Bibliography