INTERSTITIAL CELLS OF URODELE TESTIS 227 



will be filled entirely with spermatogonia, spermatocytes, sper- 

 matids, or ripe spermatozoa, but will never at any time contain 

 all of these stages, as happens in the mammalian tubuli contorti. 

 Finally, after the spermatozoa have left the lobule, it will con- 

 tain only the Sertoli cells. These do not persist, but rapidly 

 undergo degenerative changes and are in time absorbed. The 

 degenerating portion of the lobule does not contain developmental 

 stages of the germ cells ; these occur in the apex of the lobule, 

 developing as a new structure. Since the only structure common 

 to the two parts is the connective-tissue wall, the emptied portion 

 will be referred to as the emptied or degenerating 'lobule,' while 

 the mass or vesicle of spermatogonia in the apex will be termed 

 the young or regenerating 'lobule.' The former is pushed to the 

 periphery of the testis by the rapid development of the young 

 lobule in some urodeles. This McGregor ('99) states as the case 

 in Amphiuma, in which "a testis examined shortly after the 

 breeding time shows a rapid cell proliferation from the center, 

 which is to form the new 'tubules,' while the remains of the old 

 'tubules,' filled with the debris of degenerating tissue, are seen 

 in the peripheral portion. " 



A brief discussion of the changes in external form of the testis 

 seems not inappropriate at this point. It is evident that both 

 size and shape of the organ at any time will depend upon the 

 state of development of its component lobules. Urodeles possess 

 a decided cephalocaudal differentiation of the testis; a spermato- 

 genetic 'wave,' as noted by numerous investigators, passes from 

 the caudal to the cephalic end of the organ. This Svave' may 

 be rapid in its progress, in which case there results comparatively 

 little regional differentiation of the testis, as in Necturus ; it may, 

 on the other hand, be comparatively slow in its movement, in 

 which event regional differences become more pronounced. 

 This latter condition prevails in the testis of Salamandra macu- 

 losa (Meves, '96), Salamandra atra, and Diemyctylus, in which 

 at the proper time of year in cephalocaudal succession, may be 

 found 'lobes' (regions composed of few or many lobules) filled 

 with spermatogonia, spermatocytes, spermatids, or mature 

 spermatozoa, with perhaps some of the most caudal lobules 



