Necturus Testis and Reproduction 63 



myoid cells resemble, both in appearance and position, those present in 

 the boundary wall of mammalian seminiferous tubules. 



Although the intervening stages of lobular development (i.e. 

 spermatocytes, spermatids) are no longer present in the testes of animals 

 at this time, it would appear that development of the interlobular cells is 

 arrested through all stages in which germ cells are present in the lobule. 

 Following spermiation, however, the interlobular cells now become less 

 elongated with rounded nuclei. Electron microscope examination of 

 these cells in N. maculosus has demonstrated that they now possess 

 abundant organelles normally associated with active steroidogenesis 

 (Pudney et al. 1983). The regressing portions of the lobules eventually 

 become surrounded by fully differentiated Leydig cells, which in cross 

 section form what has been termed the "epithelioid ring" (see Fig. 9) 

 (Humphrey 1921). This region, which occupies the peripheral part of the 

 testis, between the terminal segments of the immature lobules and the 

 testicular capsule, constitutes the newly formed glandular tissue. In the 

 caudal zone of the testis this finally becomes the glandular tissue proper, 

 which is markedly increased in volume by further hypertrophy of the 

 Leydig cells and complete regression of the lobular remnants. The glan- 

 dular tissue also becomes highly vascular with groups of Leydig cells 

 closely associated with numerous blood vessels. 



Fig. 7. Glandular tissue proper is composed of hypertrophied Leydig cells 

 (arrowheads) and degenerating remnants of seminiferous lobules (arrows). X 125. 



