g2 John H. Gerould, 



it contains larg:er alveoli and fewer granules than the inner layer. 

 These fibres are probably the product of the intense metabolic 

 activity of the inner perinuclear layer. They are apparently con- 

 tinuous with the fibrous protoplasmic processes, which begin to make 

 their appearance upon the surface of the egg at this stage. These 

 processes (Fig. 61) extend through the pores of the vitelline mem- 

 brane, or zona radiata (Fig. 2 z. r), which is meanwhile being laid 

 down as a secretion of the cytoplasm. Since the fibrous processes 

 appear simultaneously with the beginnings of the vitelline membrane, 

 one is led to the conclusion that the latter is moulded about their 

 extremities in the process of secretion, and that the pore canals of 

 the zona radiata are the result of their presence. From the fact that, 

 during the process of secretion of the zona radiata, the diameter of 

 the oocyte increases to double its size, it may be inferred that the 

 membrane is meanwhile in a plastic condition. 



The mature oocyte both in Ph. gouldii and in Ph. vulgare is 

 spherical, and 150— 180;tf in diameter. It is covered with a chitinous, 

 highly refractive vitelline membrane 3—4 n in thickness. This 

 membrane (zona radiata), as already mentioned, is perforated by 

 numerous pore-canals, from which extend flue protoplasmic processes 

 (Fig. 61). The latter form about the egg an irregular layer, usually 

 somewhat thicker than the zona radiata. They disappear at the 

 time of fertilization, when they are probably retracted into the 

 cytoplasm. In one instance I observed that they had disappeared 

 only from the vegetative half of a developing egg. I have seen no 

 indications that they are ever retained to form cilia. The eggs of 

 Ph. gouldii in mass are of a reddish brown color ; those of Ph. vulgare 

 are pale brown. 



The ovum of the smaller species which occurs at Roscoff, Ph. 

 elongatum, is ovoid, resembling a hen's egg in shape, opaque, and of 

 a higher specific gravity than that of the other two forms. It is 

 covered with a perforated yolk membrane, but no protoplasmic pro- 

 cesses extend through these pores ; transparent, nucleated, vacuolated 

 cells adhere to its surface, forming a partial follicle. 



Spermatogonia become detached in masses from the genital cord 

 in the male, and undergo their subsequent development while floating 

 in the coelomic fluid. Morula-shaped masses of sperm heads, from 

 which the tails project, may be found in the coelomic fluid of the 

 less ripe males. The structure of the spermatozoon in Ph. vulgare 

 has been described by Cuénot (1900), who states that the oogonia 



