186 LEUCKART, ON PENTASTOMUM TZNIOIDES. 
of the short and stump-like foot is rendered considerably 
easier. ‘This description apples not only to the embryos of 
Pentastomum tenioides, but also to those of P. proboscideum 
and P. multicinctum ; nay, in the latter the structural con- 
ditions of the foot are still more distinct, because the ap- 
pendages in question, with their separate parts, are nearly 
twice as large. 
When former investigators regarded the legs of the em- 
bryo of Pentastomum as made up of two successive segments, 
they were probably deceived by the inclosed chitinous rods, 
and, in particular, looked upon the peduncular process of 
the foot-coverings as the anterior contour of a separate 
segment. But although such a deception is quite possible 
in certain positions, the true state of the case will soon be 
ascertained when the parts are viewed in other and more de- 
terminate directions. 
Many zoologists appear to entertain the opinion that these 
pedal tubercles of the Pentastomum-embryo gradually change 
into the well-known claw-like appendages of the perfect 
animal in the course of its development. To such an 
assumption I was myself inclined at first, and the more so as 
the chitinous fork of the pedal tubercles really bears some 
resemblance to the subsequently developed organs of sup- 
port; and the two embryonic claws might be readily com- 
pared with the two hooks of P. denticulatum. I have, how- 
ever, by later examinations, ascertained the incorrectness of 
this hypothesis, and arrived at the conviction that the claw- 
feet of the embryos, with all their separate parts, represent an 
apparatus which vanishes entirely during the later metamor- 
phoses. In a physiological point of view, however, one may 
well compare these structures with the claw-apparatus of 
the adult animal. The coronets of spines of Pentastomum 
denticulatum are in a similar manner represented in the 
embryos by some small and delicate sete, which are found 
arranged symmetrically, but varying in number, at the pos- 
terior extremity of the caudal appendage. 
Besides the structures hitherto described, there also exists 
a roundish sucker-like indentation in the centre of the 
dorsal surface of the embryo, the bottom of which rises in 
the shape of a cross. The embryos of P. proboscidewm and 
P. multicinctum are likewise possessed of these dorsal depres- 
sions, but here they are less considerable and without the 
cross. Internal organs are not perceptible, nor can even any 
intestine be discovered, although the oral aperture is of con- 
siderable size. (I am uncertain whether there be an anus.) 
The entire parenchyma of the body consists of a tolerably 
