LEUCKART, ON PENTASTOMUM TANIOIDES. 187 
homogeneous granular material, in which, especially at the 
lower part, are distributed numerous fat-like corpuscles. 
The embryos here described are never found free in the 
sexual passages, but always remain surrounded, even in the 
lowest portions of the tract, by the coverings of the ovum, 
which are three in number, as has been quite correctly stated 
by Schubart and Van Beneden. The most exterior forms a 
clear, transparent coat, with many folds in P. tenioides, 
which is separated from the two internal tunics by a wide 
intervening space; and it is possessed of a glutinous cha- 
racter, by means of which the eggs adhere to foreign objects 
with great facility, a circumstance which in a high degree 
favours their dispersion and transplantation. In P. tenioides, 
the substance of this exterior covering is converted by the 
addition of caustic potass into a gelatinous material, which is 
dissolved under the continued action of the reagent, while 
the two interior envelopes, which are closely approximated 
to one another, remain unaltered. These two latter have a 
very delicate and brittle consistence, so as to be readily rup- 
tured by the application of pressure. This is especially the 
case with the middle covering, which is also distinguished 
from the inner by its greater thickness and yellow colour. 
Schubart says, in regard to the latter, that it is constantly 
“provided with a little opening or facet.”” According to our 
present knowledge of the mode of fertilization of animal ova, 
we might perhaps interpret this statement to imply that the 
ova of Pentastomum are provided with a micropyle; but the 
apparent opening is in reality anything but a micropyle. An 
investigation of the previous stages of development soon 
shows that the entire innermost coat, together with the 
structure under consideration, only makes its appearance a 
long time after the fertilizing act, and in such a peculiar 
manner, that it might perhaps with perfect justice be re- 
garded as an embryonic membrane. Only the ova contained 
in the last fourth of the vagina permit us to recognise the 
three coats above described, while the others present only 
two of them, which subsequently become the middle and 
internal coverings. In the first or anterior part of the 
vagina the coats are moreover only thin and extensible, and 
lie closely upon one another, the exterior one also presenting 
a different granular character. All these are circumstances 
which render the process of fertilization intelligible even 
without a micropyle. 
The first signs of the commencing development of the 
embryo consist in a segmentation of the yelk, which, how- 
ever, at an early stage, generally immediately after the first 
VOL. VII. Q 
