THE STRUCTURE OF FREE-MARTIN GONADS 115 



with certainty, owing to the absence in the ovary of a more 

 or less distinct hne of demarkation between an inner epitheUal 

 mass (medullary cords) and an outer epithelial mass (cords of 

 Pflijger). Although the separation of the two regions is not 

 obvious in the late foetal stages of the cat's ovary, these regions 

 are distinct in the earlier stages, owing to the growth of a distinct 

 primary tunica albuginea between the two (Sainmont, '05). 

 In the ovary of both the cat and man the sexual cords of the 

 medulla take no part in the formation of ova in the fully devel- 

 oped ovary, and in this respect resemble other mammalian 

 ovaries, where the homology has not been questioned (as in 

 cattle; fig. 3, to). Furthermore, in both cases occurs the rete 

 ovarii, the undoubted homologue of the rete testis. These 

 facts are certainly sufficient to indicate that the ovarian-medulla- 

 testis homology applies in the cat and man. 



Fortunately, in the free-martin, nature has performed a veri- 

 table crucial experiment, which demonstrates without question 

 that the ovary possesses structures which have their morpholog- 

 ical equivalents in the testis. That they are morphologically 

 equivalent is shown by the transformation of certain ovarian 

 structures into testicular structures under the influence of sex 

 hormones. The following homologies are established: 1) The 

 medullary cords precisely and definitely transform into semi- 

 niferous tubules. 2) The rete ovarii transforms into a rete testis 

 chiefly by developing connections with the seminiferous tubules 

 and with the vasa efferentia. 3) The primitive tunica albuginea 

 of the ovary becomes the tunica albuginea of the free-martin 

 gonad. 4) Associated with the embryonic ovary is an epididy- 

 mal primordium which transforms into a typical epididymis. 



If a comparison of the sex-cord region of the free-martin is 

 made with certain well-known changes in the sex-cord regions 

 of mammalian testes, marked structural similarity is seen. In 

 both, the interstitial cells are hypertrophied and each seminif- 

 erous tubule has a thickened wall within which is a Sertoli-cell 

 syncytium free from germ cells. Such changes are present in 

 cryptorchid testes (Whitehead, '08, and Hanes, '11), and are 

 experimentally produced in the following ways: exposure to 



