Gametogenesis in Cestodes. 
423 
b) Formation of the cytophore. 
At an early stage in testis development the spermatogonia fuse to 
form a syncitium or cytophore (figs. 8 and 10). The stage at which this 
fusion occurs appears to vary in different species, and possibly also in 
different individuals, altho this is a point to which I have given no special 
attention. The process in any event may occnr very early for I have 
coimted as few as seven nuclei in one cytophore of Rhyncobothrinm bnlbifer. 
The early spermatogonia usually appear in groups of two, four, eight 
etc. This regularity of division is hardly what might be expected to resiilt 
from the formation of nuclei from chromidia. It does not always occnr 
however, nor does it prove anything one way or another regarding the 
method of division. 
c) Growth of spermatogonia and skein formation. 
Coincident with, or shortly subsequent to the cytophore formation 
the sperniatogonial nuclei enlarge more or less, the chromatin, which 
heretofore has been present as a nucleolus, assumes the form of a broken 
irregulär skein, and the nuclear membrane, if present, disappears, leaving 
the skeins, or better skein fragments lying free in the cytophore (figs. 9, 
11 and 15). IVhether the skein actually is broken or continuous at first I 
hesitate to say positively, because of the possibility that the apparently 
broken condition may be an artifact due to the action of the fixative; In 
many cases the skein is crowded to one side of the nucleus — evidently the 
result of shiünkage. The question is immaterial in any event. Düring 
development the skeins thicken and shorten somewhat, so that one may 
speak of “dose” and “loose skein” stages. The distinction is not well 
marked in the spermatocytes however. In the oocytes, which are much 
larger, the distinction is clearer. 
It is at this time that mitosis has been described by both Child and 
Harman as occurring niost commonly in the testis. Both of these authors 
describe first and second spermatocytic divisions, but save for a slight 
possible difference in size there is no evidence to show which is which. 
Nor do either of these authors discuss this point, contenting themselves 
with the mere assertion that both divisions occiu’. I have found mitoses 
in the testis at this time, but cannot always be certain whether they are 
those of spermatogonia or spermatocytes. Clu-omatin counts are exceed- 
ingly difficult in cestode cells, as Child has already emphasized; and there is 
furtherconsiderable evidence indicatingavariationinchromosome number^). 
^) See my previous paper (1913, p. 391 — 392). 
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