THE MULTIPLE TESTIS OF URODELES. 51 



The caudocephalic movement of the spermatogenetic processes, 

 or, as it has been appropriately termed, the spermatogenetic wave, 

 varies greatly in rate with the species of urodele considered. In 

 Amblystoma and Cryptobranchus it is comparatively rapid. As a 

 result all regions of the testis tend to be in approximately the same 

 stage of development at any particular time. In other urodeles, 

 such as Nccturus or Gyrinopliilns, the rate is considerably slower, 

 and in these several developmental stages will usually be encoun- 

 tered in cephalocaudal succession. Finally, in Desmognathus and 

 Dicmyctylus the rate is extremely slow, the spermatogenetic wave 

 traversing only a part of the length of the testis in any one sexual 

 cycle. 1 At a certain period in the cycle the secondary spermato- 

 gonia toward the anterior end of the organ cease to transform into 

 spermatocytes I. A few lobules of these spermatogonia may de- 

 generate entirely or in part, as described by Kingsbury and Hirsh 

 ('12). These degenerated lobules mark a "boundary plane" 

 caudal to which, in the current season, all the reproductive cells are 

 matured as spermatozoa. Anterior to this boundary plane the 

 germ cells are held over until the following season, when the wave 

 resumes its forward movement from the point at which develop- 

 ment was checked in the preceding season. 



The testis of Desmognathus, then, is characterized by a slow 

 movement of the spermatogenetic wave. Consider, now, the action 

 of this factor, in connection with delayed lobule regeneration, as to 

 possible effect on the structure of the testis. The testis of Plctho- 

 don, which is always of unit structure, may be used for comparison 

 with that of Desmognathus, since the two agree in possessing a 

 central 2 longitudinal collecting duct round which the lobules are 

 arranged as are the spokes of a wheel. The two are in contrast, 

 however, both as to the rate of the spermatogenetic wave and the 

 rapidity of lobule regeneration, after extrusion of the spermatozoa. 

 In Desmognathus both processes go on slowly ; in Plcthodon both 

 proceed with comparative rapidity, especially the processes of 

 lobule regeneration. 



1 The urodele male, it will be recalled, completes but one sexual cycle 

 annually. 



2 The collecting duct in Desmognathus may, however, be more or less 

 superficial towards the ends of the enlargement or lobe. 



