Gametogenesis in Cestodes. 
425 
with what I believe to occur in cestodes. It is perhaps significant that 
both types are parasites. In any event niy observations do not stand 
alone. 
e) Development of Spermatozoa. 
The method of sperni development is difficult to determine, and is 
furthermore apparently subject to Variation. The details of the process 
in Taenia pisiformis have been given by me in a previous paper (Young, 
1913), so that at this time I need only add my observations on additional 
material, which are I believe corroborative of those already published. 
I wish first of all to emphasize the simplicity of sperm structure, to 
which I have already called attention^). I have carefully examined, in both 
the living and fixed condition, the sperms of Taenia pisiformis and teniae- 
formis, Dipylidium caninnm, and Ehyncobothiium bulbifer, and in none 
of them is there any evidence of a head whatsoever. The sperms are very 
long2) and just behind the anterior end their diameter appears to be slightly 
greater than posteriorly. They taper to a point at either end without any 
visible differentiation anywhere. The sperms are motile, and I have 
occasionally seen a sperm doubled upon, and twisted about itself, with 
a small loop at one end; which condition niight, if misinterpreted, lead 
to the conclusion that the loop was a head, with a spiral filament twisted 
about the remainder. Occasionally I have seen such a sperm unwind 
itself and twist in the reverse dkection. Such apparent simplicity of 
structure is readily comprehensible if my observations on the method of 
sperm development be correct. 
Following, or in some cases possibly just prior to the forniation of 
a cytophore, and the dispersal of the skein fragments thru it, the sperms 
arise from its periphery, or apparently in some instances in the mass of 
the cytophore itself. In living material the fornier is generally the case. 
The first appearance of the sperm is in the form of a small projection or 
outgrowth from the cells of the cytophore, which in living material cannot 
be identified as first or second spermatocytes, but which in niost cases 
are probably the latter (figs. 23 and 24). To this outgrowth there is no 
evident contribution from the nucleus. It is probable however, judging 
from stained preparations, that chromatin does find its way from the 
nucleus into the developing sperm. Thus in fig. 7 o: is shown a developing 
sperm attached to a small granulc in the cytoplasm of a spermatocyte, 
1) (1. c., p. 380). 
2) 4 sperms of Dipylidium caninum averaged approximately 140 n and 7 of Taenia 
leniaejormis 130^. 
