Some Points in tlie Sj^Minatof^enesi.s of Mannnalia. ] ;-j;} 



with the above'). Previous to the first reduction division the number 

 of the chromosomes considei-ed singly is, in this animal, certainly double 

 that of the somatic cells, and during mitosis the number is reduced 

 by one half. But I am not at all satisfied that any further division 

 occurs; and whether it does or does not, there is nothing equivalent 

 to a transference of undivided chromosomes between daughter elements. 



Prior to the longitudinal division in the testis-cell of the rat, tlie 

 number of its chromosomes is by no means easy to ascertain. Ave- 

 rages of very numerous readings of the astral figure give it as 

 sixteen, and Hermann speaks of sixteen as normal to the mitosis of 

 the mouse. 



The longitudinal division itself is apparently homotype, while the 

 last mitosis which converts the growing cells into what we may term 

 spermatids is markedly hetrotype; and the number ot the chromo- 

 somes, both before and after this final division is always eight. 



From these considerations, I think that we are probably right in 

 regarding the two last divisions in mammalian spermatogenesis as 

 equivalent to the invertebrate ,,Reductions-Teilung"'; but if so, they 

 appear to me more nearly comparable to that described among vege- 

 table structures by Strasburger, Guignard, and others, hecause there 

 is no such thiiig as a direct traiismigratiou of chromosomes in amj 

 mammalian spermatogenesis with which I am acquainted. The question 

 naturally, follows (I) does the mammalian spermatogenesis stop short 

 before this stage, and does the last division of the mammal correspond 

 to the first reduction division of the nivertebrate? or (II) is the more 

 elaborate process of the lower type dispensed with, and is the necessary 

 equation between the male and female nuclear conditions brought 

 about in a more direct and a simpler fashion? Neither of these 

 suppositions can well be brought into accordance with existing ^iews. 

 If the „Reductions -Teilung", as ordinarily understood and as the 

 appearances to which I have alluded in Branchipus seem to indicate, 

 is not universal among invertebrates, then the equivalent mammalian 

 phenomena correspond exactly with this (?) abnormal invertebrate type. 



Cf. Qu. Jour. Micr. Sci. Vol. XXXV. p. 259. 



