188 LEUCKART, ON PENTASTOMUM TENIOIDES. 
division, becomes irregular and is on the whole not very 
conspicuous, since the yelk-masses never separate from each 
other into distinct globular forms. After the segmentation 
is completed, the yelk resumes pretty much its former fine- 
granular appearance, only that it is now become more trans- 
parent. A distinctly cellular structure is scarcely to be 
observed in this case, but no doubt, not so much because it 
is wanting, as on account of the cells having only a very 
small size and a tolerably homogeneous character. 
While the yelk of the Pentastomum originally fills the 
whole internal cavity of the oval egg, it subsequently con- 
tracts after the segmentation 1s completed, so that an inter- 
mediate space is formed between it and the contiguous coat. 
(The character of these coats is now what it will be afterwards, 
and the external is likewise already transparent and distant.) 
At the same time the surface of the yelk exhibits a well- 
defined, almost membranous border. In the middle of the 
part which subsequently becomes the dorsal surface, there 
appears a shallow saddle-shaped indentation. Where this 
depression is deepest, the membranous surface of the yelk 
thickens into a clear conical process, which projects, com- 
paratively speaking, to a considerable depth into the sub- 
stance of the granular yelk. 
At this stage of development the ovum of the Penta- 
stomum remains for a long time, as we may conclude at least 
from the circumstance that more than two fifths of the 
vagina are filled with ova in this stage. (In P. oxycephalum, 
from the lung of the Kaiman, investigated by myself, the de- 
velopment of the ova does not appear to make any further pro- 
gress in the vagina of the parent; at least, no later stages of 
growth could be observed in a dozen of these animals.) At 
the commencement of the last third of the vagina, the dorsal 
process just described assumes an hour-glass form; it is 
divided by a circular groove into an upper and lower half, 
the former of which, with its margins, passes directly over 
into the limiting surface of the yelk, which in the mean time 
is becoming more and more distinctly membranous. At the 
same time may be observed opposite the dorsal process, in 
the middle of the part that afterwards becomes the ventral 
surface, a transverse groove, by which it is divided into an 
anterior and posterior zone. The membranous boundary of 
the yelk-mass does not take part in the formation of this 
groove, on the contrary it extends across it like an arch, so 
that in the place in question a little intervening space is 
formed between. the yelk-mass and the previously closely 
