120 The Spermatogenesis of Desmognathus Fusca 



mantle fibers, which seems to me quite inadequate as an explanation 

 from the conditions in Desmognathus. 



The chromatin changes in Desmognathus, considered by themselves 

 and briefly stated, are as follows: The chromosomes, twelve in number, 

 (presumably) one-half that of the somatic mitoses, develop as horse- 

 shoe-shaped threads, the free ends pointing toward the idiozome. 

 These split longitudinally and incompletely, the ends being fused and 

 open out to form rings in the manner typical in Amphibia. In the 

 anaphase, however, the fused ends separate and daughter-V's are 

 formed. As these pass to the poles, a secondary splitting takes place, 

 which (presumably) masked in the late anaphase, reappears in the ex- 

 pansion of the nucleus of the spermatocyte of the second order, when 

 the chromosomes are found to be united at their apices. These united 

 V's shorten and thicken to fotm crosses and X's, which in the meta- 

 phase separate into the two component V's. In my preliminary paper 

 was set forth a discussion of the chromatin changes in view of the 

 possibility of a " reducing " division in Desmognathus, and a portion of 

 what was then said may be repeated here. It was there pointed out 

 that the formation of the crosses in the spermatocyte of the second 

 order and their subsequent solution into V's introduced the possibility 

 of a reducing division, since it was not possible to determine in what 

 plane the separation into V's took place. Granted the V's represent 



bivalent chromosomes, the result of the splitting and cross formation 



a h ^ 



gives ^ If the separation into V's simply completes the longitudinal 



c d • ha 



splitting, we have ^ and no reducing division; if, however, it takes 



V 



place at right angles the resulting V's are j^ and the division is a 



Z) a 

 "reducing" divisions. To quote from that article, 99: "If the second 

 division in Desmognathus is to be looked upon as a reducing division, it 

 may be considered in two ways. The original union of the chromo- 

 somes, after two longitudinal splittings of the united chromosomes, is 

 now dissolved and a new union between the daughter-chromosomes 

 established; or, from the standpoint of the more typical mode of reduc- 

 tion by tetrad formation with longitudinal and transverse divisions, there 

 would occur in Desmognathus, a reduction in number to one-half, a 

 longitudinal (equation) division, which, however, is not completed, and 

 is prevented from being completed, by the second division, which is 

 transverse. Shorten the interval elapsing between the first and the 

 second divisions, and (possibly thereby) eliminate the second longitu- 



