BEHAVIOR OF THE GAMETES 221 



factor (or factors) and thus frees certain morphogenetic or develop- 

 mental conditions within the egg or within a cell. Once the inhibiting 

 or blocking condition is overcome, differentiation and growth begin. 

 (9) Finally, the work on artificial parthenogenesis has demonstrated that 

 the egg is an organized system which, when properly stimulated, is 

 able to produce a new individual without the aid of the sperm cell. 

 This does not mean that the sperm is not an important factor in normal 

 fertilization, but rather, that the egg has the power to regulate its 

 internal conditions in such a way as to compensate for the absence 

 of the sperm. 



D. Behavior of the Gametes During the Fertilization Process 



The activities of the gametes during the fertilization process may be divided 

 for convenience into two major steps: 



( 1 ) activities of the gametes which bring about their physical contact with 

 each other, and 



(2) activities which result in the actual fusion of the gametes after this 

 contact is made. 



Before considering these two major steps, we shall first observe certain of 

 the characteristics of the two gametes when they are about to take part in 

 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. In the case of most animal species, the 

 female gamete is in the oocyte stage when it enters into the fertilization 

 process. (See Chap. 3; also fig. 137.) In the dog and fox the female gamete 

 is in the primary oocyte stage, and both maturation processes happen after 

 sperm entrance (fig. 115). In the protochordate, Styela, the first maturation 

 spindle already is formed when the sperm enters (fig. 116A-D), and in 

 Amphioxus the first polar body has been given off, and the second matura- 

 tion spindle is developed when the sperm enters (fig. 117A-D). The last 

 condition probably holds true for most vertebrate species (figs. 1 18B; 1 19D). 

 However, in the invertebrates, the sea-urchin egg experiences both maturation 

 divisions normally before sperm entry. 



2) Inhibited or Blocked Condition. When the female gamete thus reaches 

 a state of development determined for the species, its further development 

 is blocked or inhibited, and its future development depends on the circum- 

 vention of this state of inhibition. If not fertilized or artificially aroused when 

 this inhibited state is reached, the oocyte or egg begins cytolysis. Eggs ferti- 



