116 Embryonic Development of Ovary and Testis of Mammals 



course to accommodate itself to the large rounded projections com- 

 prising the cords of Pfliiger. These cords are still attached to the 

 peritoneum by their narrow basal portions. 



The medullary and rete tubules are usually two cells wide and with- 

 out any trace of a lumen. Their nuclei are oval and ra'ther uniform 

 in size. Here and there one finds primitive sex cells singly or in 

 groups of two to four. They are frequently in the same stage of 

 synapsis as are the more advanced nuclei of the cortex. 



In the 26-day female embryo the Wolffian duct has almost disap- 

 peared by degeneration, together with the great bulk of the urinifer- 

 'ous tubules. In the female, 10 days after birth, the mesonephric 

 structures are found to have completely degenerated save for a few 

 vestiges of uriniferous tubules lying within the rete tissue and the 

 mesentery, posterior to the hilum. Aside from these vestiges, the 

 mesonephros consists of loose connective tissue enclosing great masses 

 of fat — the remains of former Malpighian corpuscles and mesonephric 

 tubules. 



13 Days after Birth. Ovary. — Follicles are forming in the cortex 

 at this stage. They are, of course, very s^ple, each consisting of a 

 large oocyte surrounded by a single layer of granulosa cells. Exactly 

 similar follicles are also found in the medullary cords. 



Very many nuclei in all parts of the cortex and medullai-y cords are 

 suffering karyolytic degeneration. 



17 Days after Birth. Ovary. — The process of follicle formaition 

 has continued, resulting in the breaking up of the inner ends of the 

 cords of Plliiger. No sex cells are found in the medullary cords from 

 this stage on. The ova of certain of the innermost follicles have dis- 

 appeared, leaving clumps of follicle cells such as are found in corres- 

 ponding stages in the pig. Frequently one finds two or even more 

 oocytes in the same follicle. 



24- Days after Birth. Testis. — This stage shows the testis to have 

 pretty largely assumed the characters prominent in adult life. The 

 caput epididymis is made up of the much-contorted tubules of the 

 rete efferentia, the latter being traceable down to their points of con- 

 nection with the rete testis. This, as already stated in the" descrip- 

 tion of previous stages, is made up of a mass of anastomosing rete 

 tubules from which proceed the tubuli recti that connect Avith the 

 seminiferous tubules. In the posterior two-thirds of the testis, the 

 rete is wholly surrounded by the seminiferous tubules that have closed 

 in around it. Here and there primitive sex cells (spermatogonia) can 

 still be found in the rete testis. 



