CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANCHS. 3038 
in § 44, it will be seen that the former differs from the 
latter only at the beginning and the end. These differences 
are produced by the shortening up of the generations of the 
first spermatogenetic period in mammals, (a) into what is 
practically a kinetic budding, so that there is only one distinct 
homotype division with sixteen chromosomes (I, 16) before 
the synapsis ; (6) (equal growing cells) in which the chromatic 
individuals are reduced or fused together into eight. The 
process of transformation and the succeeding heterotype cor- 
respond exactly with that of the Elasmobranchs. But the 
daughter-elements produced do not, as in Elasmobranchs, 
divide again. They are converted directly into spermatozoa, 
and it thus appears that one of the two generations of ciliated 
cells, present after the heterotype in Elasmobranchs, in some 
mammals is unrepresented. 
50. Brauer,! as I have said, in his admirable account of the 
spermatogenesis of Ascaris, published in 1891, also denies 
the existence of the “ Reductionstheilung ” described by O. 
Hertwig, both in the uni- and bivalent form of this curious 
worm. There is a period of cell multiplication, equivalent to 
the first spermatogenetic period, with two or four chromo- 
somes, as the case may be, and in the divisions of which, as 
Professor Brauer has recently informed me, the chromosomes 
split longitudinally, like those in ordinary divisions. Then a 
period of rest, equivalent to the rest of transformation, in 
which the number of the chromosomes is halved, followed by 
divisions of a totally different character, in which there 
appears to be precocious splitting of the chromatic elements 
and rapid separation of daughter-cells,? without the nuclei 
1 Loe. cit. 
? It is probable that all the cases of the so-called “ Reductionstheilung ” are 
in reality referable to a process of precocious splitting among the chromosomes, 
whereby the elements for several daughter-cells are produced at once, and are 
then distributed, either by successive divisions without rest, or by multipolar 
spindle formation. An admirable example of the latter method is afforded by 
Farmer’s description of the spore formation in Pallavicinia decipiens. 
In these plants the number of the chromosomes in the sporophyte genera- 
tion is always eight, but as soon as the spore mother-cells are formed, the eight 
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