110 Embryonic Development of Ovary and Testis of Mammals 



tion of the ovary, made up of loose connective tissue (stroma) -which 

 extends between the cords of Pflliger in the form of strands and plates 

 having a texture denser than that of the central mass. These strands 

 are continuous with a sub-peritoneal layer of connective tissue that 

 separates the cords of Pfliiger from the peritoneum, thus putting an 

 end to their further growth at the expense of the latter. Here and 

 there a slender ingi'owth from the peritoneum is still found to pierce 

 the connective tissue layer, yet these are of slight importance. I am 

 not prepared to say whether they assume greater importance in later 

 stages. 



The cortex contains sex cells in all stages of development, from 

 the very young oogonia of the peripheral region to the small follicles 

 in its innermost edge. The remains of the medullary cords and of 

 the intra-ovarian portion of the rete are still present in the medullary 

 region and are fomid to be in practically the same condition as in the 

 20 cm. embryo. Not a sign of sex cells is to be seen in either the 

 intra- or extra-ovarian portions of the rete. 



The rete tissue is much more extensive in this stage than in the 

 20 cm. stage. There it was again more extensive than in the preced- 

 ing (18 cm.) stage). Although these observations would seem to 

 point to its growth after the degeneration of the sex cells, one should 

 not lay too much stress upon this point. These seemingly conclusive 

 facts may be conditioned l^y the great variability universally seen to 

 exist in vestigial structures. A study of the rete cells failed to reveal 

 extensive nuclear division in the above stages. 



IV. DETAILS OF DEVELOPMENT IN THE EABBIT. 



13-Day Embryo. — There is at this stage no obser^^able difference 

 between the structure of the sex gland and rete rudiments. This 

 stage corresponds with the 0.8 cm. stage of the pig. One is struck 

 with the vagueness of the basement membrane of the peritoneum both 

 in this and in succeeding stages of the rabbit, yet it is as tridy present 

 as in the pig embryos where it appears with remarkable distinctness. 

 Many of the cells of both stroma and peritoneum are found to be 

 quite -irregular in shape, in many cases even amoeboid. Frequently 

 they appear to be dividing by amitosis. It is very difficult to decide 

 whether this be merely apparent or real. This point deserves special 

 study, as it is of prime importance. A few figures of mitosis appear 

 here and there. Primitive sex cells are present, though rare, occurring 

 either in the peritoneal layer or beneath it. They are to be distin- 

 guished from the surrounding peritoneal and stroma cells l)y the same 



