88 Vertebrate Embryology 



be, develop, while from the anterior third the 

 fat bodies are developed. 



The genital ridge is primarily formed by the 

 change in the shape of the cells of the perito- 

 neal epithelium at that place. While most of 

 the epithelial cells of the peritoneum are flat, 

 those that are to form the genital ridge become 

 more cuboidal or columnar, at the same time 

 dividing and becoming several cells deep ; a 

 vascular core of connective tissue now grows 

 into the genital ridge from the basement mem- 

 brane of the peritoneum. 



Some of these epithelial cells grow more 

 rapidly than the rest and become spherical in 

 shape, while the smaller cells collect around 

 the large ones to form capsules or follicles. 

 The large round cells are known as primi- 

 tive germ cells or gonoblasts, and from them 

 are developed, at the time of metamorpho- 

 sis, when the sexes become differentiated, 

 either true oiia or eggs, in the case of the 

 female, or spermatozoa, in the case of the 

 male. 



The limits of this work will not permit a de- 

 scription of the histological changes that take 

 place in the conversion of the primitive ova 

 into the true sexual elements, and, indeed. 



