Bennet Mills Allen 



115 



nuclei are arranged side by side, usually in a single layer, although 

 one, at times, finds a superposed layer. A few primitive sex cells occur 

 in the portion of the rete tissue lying within the testis. A complete 

 series of transitional forms are found to connect the primitive sex 

 cells with the germinative cells in this as in the 17, 21, 23 and 26- 

 day stages. 



In both male and female the me- 

 sonephros proper has almost wholly 

 disappeared, leaving a connective tis- 

 sue network in whose meshes lie masses 

 of fat. The caput epididymis (Text 

 Fig. 4), made up of contorted tubules 

 (rete efferentia) lined with epithelial 

 cells, still remains. These are the 

 persistent uriniferous tubules of the an- 

 terior part of the mesonephos, the great 

 bulk of the tubules posterior to these 

 having degenerated, together with a 

 few of those which were formed in the 

 most anterior end of the mesonephros. 

 A few shrunken glomeruli still persist 

 in connection with the rete efferentia. 



Rahhit 3 and 8 Days after Birth. 

 Testis. — These stages are interesting 

 chiefly because they show a marked 

 diminution in the number of inter- 

 stitial cells which, however, are still 

 found to be in process of division by mitosis. 



Rahhit 10 Days after Birth. Ovary. — The rete tubules are in all 

 cases devoid of a lumen. They are frequently joined to hollow 

 tubules of larger diameter which extend into the general rete mass. 

 These are the rete efferentia. Their identity is shown by the large 

 size of the lumen, and by the fact that the nuclei are larger than those of 

 the rete tubules. These rete efferentia have been brought to lie within 

 the hilum by the extension of the ovary to partially enclose the 

 shrunken mesonephros. They probably grow into the ovary of their 

 own account as well. The differences between medullary cords and 

 rete tubules disappeared as far back as the 23-day stage of embryonic 

 life. 



The cortical layer is distinctly bounded from the medullary sub- 

 stance by a dense layer of connective tissue which follows a zig-zag 



■"Fir.. 4. .Sagittal section of the testis 

 of the rabbit, 3 days after birth, al., al- 

 buginea ; m., mesonephric remains; ?•., 

 rete ; r. e., rete efferentia ; s. tu., semi- 

 niferous tubule ; W. d.. Wolffian duct, 

 X28. 



