Book - Comparative Embryology of the Vertebrates 2

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Nelsen OE. Comparative embryology of the vertebrates (1953) Mcgraw-Hill Book Company, New York.

   Comparative Vertebrate Embryology 1953: 1. The Period of Preparation | 2. The Period of Fertilization | 3. The Development of Primitive Embryonic Form | 4. Histogenesis and Morphogenesis of the Organ Systems | 5. The Care of the Developing Embryo | Figures
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Part II - The Period of Fertilization

Part II - The Period of Fertilization: 4. Transportation of the Gametes (Sperm and Egg) from the Germ Glands to the Site where Fertilization Normally Occurs | 5. Fertilization

The period of fertilization involves:

  1. The transportation of the gametes to the site normal for the species where environmental conditions are suitable for gametic union (Chap. 4), and
  2. Fertilization or the union of the gametes (Chap. 5).

The union of the gametes may be divided into two phases, viz.:

  1. The primary phase which is terminated when the sperm has made intimate contact with the egg's surface, and
  2. The secondary phase or the fusion of the two gametes resulting in the initiation of development.

Transportation of the Gametes

4. Transportation of the Gametes (Sperm and Egg) from the Germ Glands to the Site where Fertilization Normally Occurs

A. Introduction

1. Activities of the male and female gametes in their migration to the site of fertilization

B. Transportation of the sperm within the male accessory reproductive structures

1. Transportation of sperm from the testis to the external orifice of the genital duct in the mammal

a. Possible factors involved in the passage of the seminal fluid from the testis to the main reproductive duct

1) Accumulated pressure within the seminiferous tubules

2) Activities within the efferent ductules of the testis

b. Movement of the semen along the epididymal duct

1) Probable immotility of the sperm

2) Importance of muscle contraction, particularly in the vas deferens

3) Summary of factors which propel the seminal fluid from the testis to the external orifice of the reproductive duct in the mammal

2. Transportation of sperm in other vertebrates with a convoluted reproductive duct

3. Transportation of sperm from the testis in vertebrates possessing a relatively simple reproductive duct

C. Transportation of sperm outside of the genital tract of the male

1. Transportation of sperm in the external watery medium

2. Transportation of sperm in forms where fertilization of the egg is internal

a. General features relative to internal fertilization

1) Comparative numbers of vertebrates practicing internal fertilization

2) Sites or areas where fertilization is effected

3) Means of sperm transfer from the male genital tract to that of the female

b. Methods of sperm transport within the female reproductive tract

1) When fertilization is in the lower or posterior portion of the genital tract

2) When fertilization occurs in the upper extremity of the oviduct

3) When fertilization occurs in the ovary

D. Sperm survival in the female genital tract

E. Sperm survival outside the male and female tracts

1, In watery solutions under spawning conditions

2. Sperm survival under various artificial conditions; practical application in animal breeding

F. Transportation of the egg from the ovary to the site of fertilization

1. Definitions

2. Transportation of the egg in those forms where fertilization occurs in the anterior portion of the oviduct

a. Birds

b. Mammals

3. Transportation of the egg in those species where fertilization is effected in the

caudal portion of the oviduct or in the external medium

a. Frog

b. Other amphibia

c. Fishes

G. Summary of the characteristics of various mature chordate eggs together with the site of fertilization and place of sperm entrance into the egg


5. Fertilization

A. Definition of fertilization

B. Historical considerations concerning gametic fusion and its significance.

C. Types of egg activation

1. Natural activation of the egg

2. Artificial activation of the egg

a. Object of studies in artificial parthenogenesis

b. Some of the procedures used in artificial activation of the egg

c. Results obtained by the work on artificial parthenogenesis

D. Behavior of the gametes during the fertilization process

1. General condition of the gametes when deposited within the area where fertilization is to occur

a. Characteristics of the female gamete

1) Oocyte stage of development

2) Inhibited or blocked condition

3) Low level of respiration

4) Loss of permeability

b. Characteristics of the male gamete

2. Specific activities of the gametes in effecting physical contact of the egg with the sperm

a. Activities of the female gamete in aiding sperm and egg contact

1) Formation of egg secretions which influence the sperm

a) Fertilizin complex

b) Spawning-inducing substances

b. Activities of the male gamete in aiding the actual contact of the two gametes

1) Sperm secretions

a) Secretions producing lysis

b) Secretions related specifically to the fertilization reactions

c) Secretions which induce the spawning reaction in the female

2) Relation and function of sperm number in effecting the contact of the sperm with the egg

3) Influences of the seminal plasma in effecting sperm contact with the egg

4) Roles played by specific structural parts of the sperm in effecting contact with the egg

a) Role of the flagellum

b) Role of the acrosome in the egg-sperm contact

5) Summary of the activities of the egg and sperm in bringing about the primary or initial stage of the fertilization process, namely, that of egg and sperm contact

3. Fusion of the gametes or the second stage of the process of fertilization

4. Detailed description of the processes involved in gametic union as outlined above

a. Separation and importance of a protective egg membrane, exudates, etc.

b. Fertilization cone or attraction cone

c. Some changes in the physiological activities of the egg at fertilization

d. Completion of maturation divisions, ooplasmic movements, and copulatory paths of the male and female pronuclei in eggs of various chordate species

1) Fertilization in Styela (Cynthia) partita

a) Characteristics of the egg before fertilization

b) Entrance of the sperm

c) Cytoplasmic segregation

d) Copulatory paths and fusion of the gametic pronuclei

2) Fertilization of Amphioxus

3) Fertilization of the frog’s egg

4) Fertilization of the teleost fish egg

5) Fertilization in the egg of the hen and the pigeon

6) Fertilization in the rabbit

7) Fertilization in the Echidna, a prototherian mammal

E. Significance of the maturation divisions of the oocyte in relation to sperm entrance and egg activation

F. Micropyles and other physiologically determined areas for sperm entrance

G. Monospermic and polyspermic eggs

H. Importance of the sperm aster and the origin of the first cleavage amphiaster

I. Some related conditions of development associated with the fertilization process

1. Gynogenesis

2. Androgenesis

3. Merogony

J. Theories of fertilization and egg activation