Solilo l'dinf.s in tlio Sperinat/igenesis of Miiimnaliii. 1 ;{5 



is that of the "identity of the chromosomes" duiiii}? the i-estiiif? 

 coiiditioii of the cell in general. This last supposition has been 

 completely rejected by O. Hertwig 'j on precisely the same grounds 

 which militate against the belief in a definite number of chromosomes 

 in these confused mammalian mitoses. The foregoing are however not 

 all the difficulties which have to be faced, if belief in the potential 

 existence of chromosomes in the cells in question is to be maintained: 

 because it is not here a question of the disappearance of a definite 

 number of chromosomes in the reticulae of daughter elements, but of 

 the non-forthcoming of any definite number, even in those ver}'' mitoses 

 in which, if these phenomena have any very close relation to hereditary 

 transmission, we might reasonably expect to find it. 



In many mammals there is not a really good mitosis, i. e. one in 

 which we can count the chromosomes, from beginning to end of the 

 whole spermatogenetic process; and, as I show later, radically akinetic 

 division can be apparently indiscriminately introduced at any period. 



Is it then to be supposed that some hypothetical numerical division 

 into chromosomes exists, so to speak, potentially (for it does not exist 

 actually) in these figures, simply because otherwise they do not fit in 

 with certain hypotheses, deduced from the study of species in which 

 the chromatin is separated into distinct chromosomes with almost 

 mathematical exactitude? All that can- be fairly said is that the cells 

 in question have lost some of their karyokinetic characters. This 

 mitotic degeneration is, as I shall show, a marked feature in the wdiole 

 range of mammahan spermatogenesis, sometimes occm-ring in one [)hase 

 and sometimes in another, in an apparently capricious and indefinite 

 way. I have as yet not examined any marsupial testes; but, roughly 

 speaking, with respect to those of the placentalia which have come 

 under my notice, there seems to be a progressisme development of this 

 degeneration phenomenon. The particular appearance relating to the 

 last division to which I have just referred is probably really nothing 

 new. In the accounts given by Boveri, '^) Hertwig, Ishikawa, and more 



^) loc. cit. (p. 132). 



-) „Zellenstudien", Jenaische Zeitschrift. Bd. XXIV. p. 314. 



