126 The Spermatogenesis of Desmognathus Fusca 



pretation), has moved forward from the second spermatocyte into the 

 anaphase of the primary spermatocyte. In the oogenesis of the Tritons, 

 Carnoy et Le Brun, as already stated, tind that the second splitting 

 follows the first so rapidly that by the two splittings, a chromatin ring 

 (tetrad) is formed, though sometimes the second splitting appears in the 

 anaphase of the first division. In all these cases the chromatin division 

 is by longitudinal splittings not (in this respect) markedly different from 

 those of ordinary mitoses, but becoming less typical as the resting period 

 is shortened and the chromatin fission is shifted toward the first mitosis. 

 In all, however, the intervening period of growth is inadequate to 

 restore the chromosomes to their former size, and the chromosomes of 

 the second division are markedly smaller than those of the first, pre- 

 sumably approximately one-half their size, as commented on by Moore, 

 Lenhossek, Meves, Carnoy et Le Brun. 



From the Amphibia, it is but a step to the condition described by 

 Boveri in Ascaris, where the second chromosome division, occurring 

 as a longitudinal fission before the first mitosis, forms tetrads by a 

 double longitudinal splitting, which Boveri himself interpreted as a 

 precocious splitting due to or associated with the lack of nuclear recon- 

 struction between the two divisions. 



Why it is that, in what is generally regarded as the more usual 

 method of tetrad formation, the chromatin preparation for the two 

 divisions is accomplished by the first longitudinal splittings being (in 

 the typical case) followed by a transverse splitting as the second division 

 instead of another longitudinal one, is, of course, on the basis of bur 

 present knoAvledge, entirely inexplicable. The nature of the changes 

 that go on in the cell and induce spirem and chromosome formation 

 and longitudinal fission is equally unknown, and the explanation of 

 ,why in certain forms and certain mitoses the daughter-chromosomes are 

 formed by a transverse instead of a longitudinal separation, must be 

 wrapped up with the explanation of the former; in other words, the 

 exception must be explained with the rule. Any discussion of the side 

 of mitosis, to which this leads, is beyond the scope and ambition of this 

 article, but the interpretation of the transverse division is to be sought 

 in that portion of mitosis phenomena in general. The fact, however, 

 that in the same divisions, in different forms, the separation occurs in 

 different ways, indicates that the plane of fission is not the determining 

 factor, or intrinsically important, but is itself determined by other 

 factors. Forms in which tetrad formation is accomplished by means 

 of at least one transverse division are, I believe, all forms in which 



