The Eggs of Mammals (1936) 6

From Embryology

Chapter VI The Tubal History of Unfertilized Eggs

The Eggs of Mammals (1936): Introduction | The Origin of the Definitive Ova | The Growth of the Ovum | The Development and Atresia of Full-Grown Ova and the Problem of Ovarian Parthenogenesis | Methods Employed in the Experimental Manipulation of Mammalian Ova | The Tubal History of Unfertilized Eggs | Fertilization and Cleavage | The Activation of Unfertilized Eggs | The Growth and Implantation of the Blastodermic Vesicle | Summary and Recapitulation | Bibliography | Figures | Historic Disclaimer
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When ovulation occurs without fertilization the liberated ova enter the Fallopian tubes and eventually degenerate. In most polyovular mammals the ova are shed surrounded by an apparently sticky cumulus ovigerus so that a sort of plug is formed due to the adhesion of the various separate cumuli (see Plate VI, Figure 1). This cumulus mass remains more or less intact for some time and then the cumulus cells gradually become detached so that the ova finally float free. The opossum (Hartman, 1925) and sheep (Clark, 1934) appear to be exceptions since very few follicle cells surround the newly shed ova.


The chronology of egg passage in the tubes is best had in the rabbit where ovulation occurs at 9 J^ to 10}^ hours after copulation.


The freshly ovulated ova enter the tubes and become massed together, due to the adherence of the sticky masses of cumulus cells. By 11 hours after copulation (about 1 hour after ovulation) this mass of cumulus cells containing the ova becomes securely lodged in the narrower portion of the tubes just below the broad, fimbriated end. On washing from the uterine end of the tubes this mass (see Figure 1, Plate VI) is first ejected, then the washing fluid. The ova remain thus massed together until about 17 hours after copulation, an occasional ovum separating out of the mass as early as 16 hours after copulation. Figure 2, Plate VI, is the photograph of an ovum still embedded in the mass of follicle cells at 16 hours after copulation. Figure 3 is the photograph of the single one of the 10 ova removed at the same time as that of Figure 2 that had separated out of the mass. Note a number of follicle cells still clinging to the egg.

Plate VI

(From the Proceedings of the Royal Society.)

Fig. 1, Three ova in the cumulus mass recovered from the fallopian tubes of rabbit doe 123^ hours after a sterile mating. Fig. 2, An unfertilized ovum still in the cumulus mass 16 hours after a sterile mating. Fig. 3, Another 16-hour ovum free of the cumulus mass. Fig. 4, An ovum recovered 19 hours and 5 minutes after a sterile mating with no adherent follicle cells. Fig. 5, An ovum recovered 243^ hours after a sterile mating showing a definite albumin coating. Figs. 6-9, All from sterile matings at the following intervals after sterile copulation: 6. 43 hours, 30 minutes, 7. 73 hours, 40 minutes, 8 and 9. 96 hours, 45 minutes.


As they separate out of the cuinuhis mass the egjj;s emerge surrounded more or less by a few adherent folUele cells, and proceed down the tubes where these few adherent cells are lost. At 20 hours after copulation all the adherent cells are gone and a thin layer of albumen is laid down about the zona pellucida. Eggs washed out at this time show very clearly the transparent, shining zona pellucida about the yolky, granular egg cytoplasm, with an extremely thin albumen layer surrounding the zona (see Figure 4). The process in\'oh'ing the separation of the eggs out of the cumulus mass and the clearing off of adherent cells thus involves a period of about 3 hours. When eggs are washed out during this period one observes in a single washing all the stages described, eggs completely clear of adherent cells being preponderant toward the end of the period. One may even find an occasional egg still surrounded by adherent cells as late as 20 hours after copulation.


It is important for reasons that will be obvious later, to note that by 20 hours after copulation all rabbit ova are free of follicle cells and have begun to accumulate a layer of albumen. By 24 hours after copulation this albumen lajTr is quite appreciable (see Figure 5). Subsequently the ova descend to the uterine end of the tubes acquiring in their passage successive layers of albumen so that the albumen layer may eventually become several times the thickness of the egg itself (see Figures 6 to 9). The zona pellucida no longer presents the clear, shining appearance observed before the deposition of albumen. Most of the ova recovered from the tubes contain at least one polar body, occasionally two or even three. In some cases none ha\'e been observed but this may be ascribed to faulty observation as the eggs often come to rest with the polar body hidden.


The eggs enter the uterus between 72 and 96 hours after copulation. No more albumen is added and the eggs undergo rapid disintegration. It is, in fact, very difficult to recover unfertilized ova from the uterus. Pincus (1930) was unable to obtain the full complement as indicated by the corpora lutea count. They are either rapidly resorbed or washed out into the vagina. The cytoplasm of eggs recovered from the uterus shows distinct evidences of degeneration (Figures 8 and 9).


The persistence of the corona radiata for some time after ovulation occurs regularly not only in the rabbit (cj. Yamane, 1930, 1935) but also in the mouse CLong, 1912), the rat (Gilchrist and Pincus, 1932), the dog fEvans and Cole, 1931), and man (Allen, Pratt, Newell and Bland, 1930a). It is notable that opossum ova with no surrounding cumulus mass enter the uterine portion of the oviduct in approximately twenty-four hours, whereas all available information indicates that in the higher mammals unfertilized ova entering the uterus do so at approximately 3 H days after ovulation. In the rat (and probably also the mouse) unfertilized ova apparently degenerate in the uterine portion of the tubes (Long and Evans, 1922; Mann, 1924). Albumen deposition about tubal ova occurs in the rabbit and opossum; in most other mammals the ovum traverses the tube surrounded only by the zona pellucida.


The dissolution of the cumulus mass surrounding newly liberated ova seems to involve a definite process in the tubes and is in all probabiUty not due to an autogenous change in the cumulus cells themselves. In guinea pigs the fresh cumulus mass is so tenaciously adherent that it cannot be completely removed by dissection (Squier, 1932). Gilchrist and Pincus (1932) found that rat ova incubated in Ringer's solution did not become free of adherent cells even after many hours. In rabbit ova grown in blood plasma a fibroblast-like outgrowth of the cumulus cells occurs but nonetheless the radial connections to the zona pellucida are not lost (Pincus, 1930). The writer has also observed a similar outgrowth from the cells surrounding cultured human ova, but the extremely tenacious covering of follicle cells is not lost. The likelihood that a slow enzymatic process is involved in the freeing of the adherent cells is substantiated by the great acceleration of this dehiscence in the presence of sperm (see Chapter VII).


The unfertihzed ova of most manamals begin to showsigns of degeneration when they reach the distal portion of the tubes. In the opossum clear evidences of degeneration are observed by twenty-four hours after ovulation when the ova enter the uterus (Hartman, 1924). The degenerative changes have been described in detail by Smith (1925). The ovum may remain intact but develop a well vacuolized cytoplasm with clumped or fragmented chromatin. Ordinarily, a definite fragmentation of the whole ovum occurs (Figure 20), and the irregular blastomere-like formations may contain bits of fragmented chromatin or lack chromatin entirely. In some 300 opossum ovum sectioned and examined Smith never observed a true cleavage spindle, and appropriately concludes that parthenogenetic development never occurs. Her statement that pregnant (or psuedopregnant) condition of the animals should favor parthenogenesis is not necessarily correct since activation may require special physiological conditions. In the unmated mouse, however, Charlton (1917) has described identical modes of degeneration in tubal ova with scarcely an approach to normal cleavage, and out of 152 tubal ova in the unmated rat Mann (1924) found only three which appeared to have undergone a belated parthenogenetic development (see Table VIII). In the rabbit (Pincus, 1930) fragmentation occurs rarely; an o\aim of the type shown in Figure 21 is occasionally encountered.


Fig. 20. Fragmenting opossum egg seven days after arriving in the uterus. Section of one of the eggs shown at A, containing three large chromatin masses almost free of cytoplasm. (From the American Journal of Anatomy.)


The fragmenting ova found in the tubes of rats and mice


Fig. 21. Rabbit ovum recovered from the tubes 411^ hours after sterile copulation showing polar fragmentation. (From the Proceedings of the Royal Society.)


TABLE VIII

The Conditions of Tubal Ova in Various Portions of the Oviduct IN THE Rat. (From Mann, 1924)



z

z

z ,


o ,

o

O U



?^

h>

hS




<


as J

^r,

n


^H

g


^

P <

^ ss

p £ a

03

s <

o <


^ S!

TD

H a

h O

h OS o

■t a

z a

a

^ 5

a

^

z

< <

< J

< H <

s „

^ 3

S 3

a

?^ ^

a Q

c^


IrH r\

H O


y^

^ ra

'^^ O

■^■^ K

«S

s u

Z P

^

So

J ° «

>J

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m

a E 9

lis

ii

o z

m

a z

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a

Oh


< o z a a a

H O Q Z OS 2

a a o


PhO

aixas

xnm'A

Ui'J-jU

Um

P^O

c^So

fe

hS

QUO

^

1-3.5

34

4

2

15


2


4-5

6


16

2

1


1


5-8.5

1


7

14

13

1 1

8.5-9


2



6

22


2

Totals

41

4

2

40

16

20

22

2

2

3


finally disappear either through complete disintegration or, what is more hkely, by phagocytosis (Figure 22). They usually disappear before the succeeding ovulation, although Hensen (1869) has described the retention in a blocked tube of about 100 rabbit eggs apparently from several ovulations.


Fig. 22. Section through a fragmented mouse ovum recovered 81 hours after a sterile mating. Phagocytes (C) absorb the degenerated cytoplasmic particles (E). (From the Biological Bulletin.)


The rate of passage of ova in the tubes and the method of transport have been the subject of considerable controversy and discussion (see Parker, 1931 and Hartman, 1932&). It is generally acknowledged that the passage through the upper portions of the tubes is relatively rapid (Anderson, 1927; Lewis and Wright, 1935) since except shortly after ovulation both unfertilized and fertilized ova are found for the most part in the lower two-thirds of the tube. The method of propulsion of the ova by ciliary and other tubal movements is adequately discussed by both Parker and Hartman and will not be entered into here.



Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" 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 and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)
The Eggs of Mammals (1936): Introduction | The Origin of the Definitive Ova | The Growth of the Ovum | The Development and Atresia of Full-Grown Ova and the Problem of Ovarian Parthenogenesis | Methods Employed in the Experimental Manipulation of Mammalian Ova | The Tubal History of Unfertilized Eggs | Fertilization and Cleavage | The Activation of Unfertilized Eggs | The Growth and Implantation of the Blastodermic Vesicle | Summary and Recapitulation | Bibliography | Figures | Historic Disclaimer

Cite this page: Hill, M.A. (2018, September 18) Embryology The Eggs of Mammals (1936) 6. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/The_Eggs_of_Mammals_(1936)_6

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