CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANCHS. 3805 
which have been raised, by botanists, against the numerical 
halving of the chromosomes in the resting reproductive cells 
of plants having anything in common with the Reductions- 
theilung, can be used with equal weight in the case of the 
synaptic phenomena in the animals I have just described. And 
there is yet another and much more formidable obstacle to 
such a view, namely the possibility, if not probability, of both 
the synapsis among animals and the analogous processes 
in plants being interpretable on common and quite different 
grounds. 
53. It will have been seen that throughout the whole course 
of the evolution by which the halving of the number of the 
chromosomes in the above animals is produced, there exists at 
least a superficial similarity to that accompanying the forma- 
tion of the spore mother-cells and embryo-sacs in plants; 
and Strasburger,! in the address to which I have referred 
above, has already put forward, in a more or less provisional 
way, the ingenious suggestion that the halving of the number 
of the chromosomes in the reproductive cycles of living 
organisms may be interpretable on phylogenetic and not on 
physiological grounds. This attempt, however, to bring the 
whole of the phenomena into line is sadly hampered, thanks 
to the influence of the “ Reductionstheilung ” on investigation, 
by the insufficiency of recorded observation on the zoological 
side. I am enabled now, however, with these new facts 
relating to the reproductive cycles of Elasmobranchs, to draw 
Strasburger’s comparison between animals and plants much 
closer, and to show that the phylogenetic interpretation of the 
numerical halving of the chromosomes of both is probably 
true. 
54. It will be seen on reference to § 19 of the descrip- 
tive part of this paper that the prophasis of the heterotype 
division following the synapsis in Elasmobranchs is _pre- 
ceded by a peculiar readiness of the chromatin to contract into 
forms like those represented in fig. 39, which is charac- 
teristic of this particular phase in the spermato- and ovo- 
1 Loe. cit, 
