DEVELOPMENT OF OVARY AND TESTIS. 6 1 



are most common in the region where the sex-gland will even- 

 tually form, occurring both in the peritoneum and among scat- 

 tered subperitoneal cells of mesenchymal nature. They are prom- 

 inent in the sex-cords of a later stage. In the 1.8 cm. pig 

 embryo, immediately after the separation of the sex-cords from 

 the peritoneum, the latter is found to contain no sex-cells dis- 

 tinguishable as such. If the sex-gland be an ovary, they soon 

 (2.5 cm. pig embryo) make their appearance in the .peritoneum, 

 and especially in the cords of Pfliiger growing inward from it. 

 These cords of Pfliiger increase by growth at their bases, i. e., 

 their points of connection with the peritoneum. Hence there is 

 a continual development of peritoneal cells to form the primitive 

 ova distinguishable as such. The case of the seminiferous tub- 

 ules is not so clear. Well-developed sex cells are found in them 

 from the start. On the other hand, all stages of transition are 

 found to link the germinative cells with the sex cells. These 

 transitional cells are found in the testis of the pig at as late a 

 stage as the 13 cm. embryo. 



Whether the sex-cells that appear in the very early stages of 

 embryonic development ever produce functional sex products in 

 the testis, is a question that cannot easily be solved in this form. 

 Certain it is, however, that true sex products do form in both 

 ovary and testis from apparently undifferentiated cells of peri- 

 toneal origin, and that those which are functional in the ovary 

 form exclusively from this source. The sex-glands and rete tissue 

 are the seat of extensive processes of cell degeneration. I shall 

 not here enter upon a discussion of the different forms which 

 this process assumes, but shall defer treatment of these considera- 

 tions to the more complete account. 



This piece of research has brought up many interesting facts, 

 bearing upon questions touching upon the action of trophic 

 stimuli in embryonic development. Perhaps the most striking 

 example of this is the formation of follicles in that portion of the 

 rete tissue lying within the ovary. The extra-ovarian part, or 

 that remaining in the mesonephros, does not contain follicles, 

 although it is of precisely the same origin as the intra-ovarian 

 portion. The influence of the ovary reaches out a short distance 

 into the mesonephros, as can be seen by the presence there of a 



