CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANOHS. 309 
formation of the mature sexual cells. They appear rather 
to constitute a sort of vanishing quantity, the existence of 
which becomes intelligible only on the supposition that they 
represent a phylogenetically decreasing succession of post- 
synaptic generations. 
The flagellum which I found in the first cellular genera- 
tion after synapsis in Elasmobranchs appears to me to indi- 
cate more clearly than anything I know, that the cells, 
before and after the synaptic phase, are morphologically dis- 
tinct. If the spermatogeneses of Mammalia were the only ones 
we knew, the tail developed in the generation following the 
synapsis might legitimately have been regarded as a purely 
physiological structure acquired simply to suit the exigencies 
of the case. But the fact that in Elasmobranchs the com- 
plex initial phases of tail formation (ef. § 35) are gone through 
in the first as well as the second post-synaptic generation, 
is to me quite unintelligible, unless these flagella represent 
similar structures once possessed by the representatives of the 
cells’ remote ancestry. This view is greatly strengthened by 
the complete analogy of structure which exists between the 
post-synaptic generations of Elasmobranchs and some of the 
simplest forms of sexually reproductive cells. It is well known 
that in many Algz, reproduction can be carried on by means 
of fusion between two flagellate gametes, and quite recently 
Strasburger has discovered! that the flagella of such gametes 
arise from the kinoplasm, a structure which there is every 
reason to believe is the vegetable homologue of the archoplasm. 
Moreover, among these organisms there exist species which 
exhibit every gradation between those in which both gametes 
are alike and flagellate, and others in which there is a true 
tailed spermatazoon, and a tail-less ovum. 
60. It would appear thus that if the foregoing comparisons 
are just, the existence of cellular generations with vestigial 
flagella, after the synapsis and before the spermatids have 
been formed, indicates that the synaptic phase marks a period 
in the reproductive cycle at which the cells return to a flagel- 
1 *Histolg, Beitr.,’ 1892, Heft iv. 
