458 Prof. R. Leuckart on the Developmental 
and this was probably in general overlooked (up to the time of 
Claparéde) only in consequence of its peculiar form. It consists 
of a short and plump oval body (0-049 millim. in length, and 
0:022 millim. in breadth), which occupies almost the whole 
space of the ovum, and of a thin conical tail (of 0:034 millim. 
in length) which is bent up on one side. Slender embryos, 
coiled up and moving briskly, such as occur in most Nematoda, 
and were ascribed by Vix also to Oxyuris vermicularis, have 
never been met with by me. 
The ova of Ascaris lumbricoides and Trichocephalus dispar are 
only developed after a long sojourn in water or damp earth. (I 
have never been able to bring this development to completion in 
urine and in artificially prepared pits). In the first-mentioned 
worm the separation of the embryo usually requires from four 
to six months in summer, and in the other perhaps six to eight 
months ; but the periods frequently oscillate in one or the other 
direction. Under certain conditions, the ova of Ascaris lumbri- 
coides are not developed until the lapse of more than a year. 
The embryo of Ascaris lumbricoides is much more slender than 
that of Trichocephalus, and is furnished with a short pointed tail, 
and a small tooth-like projection on the ventral side of the buccal 
orifice. It measures 0:25-0:28 millim., while the embryo of 
Trichocephalus affinis, which is rather larger than that of 7’. dis- 
par, with the same thickness (0°01 millim.), only measures 
0:127 millim. The embryos of Ascaris mystax and A. marginata, 
which inhabit the intestines of the cat and dog, and also require 
a period of several months for their incubation, although generally 
a shorter time than those of A. lumbricoides, present precisely the 
same characters, and only differ in size, the length in A. mystax 
being 0°38 millim., and in A. marginata even 0°42 millim. As, 
moreover, the egg-shells of the Nematode worms just mentioned 
possess the same thickness and resistant power, we may suppose 
that the fate of the young brood agrees with that of A. /umbri- 
cotdes. 
From the observations on other Nematoda above described, it 
might perhaps be anticipated that these embryos slip out of 
their shells when their development is completed. The shells 
are certainly thicker and firmer than in Dochmius, for example ; 
but nevertheless such an assumption cannot be regarded @ priori 
as erroneous—and this least of all with respect to Tricho- 
cephalus, the egg-shells of which bear an orifice at each pole, 
closed by a soft, nearly albuminous substance, like a stopper, 
which might easily be removed by the pressure of the worm. 
In Ascaris, indeed, these orifices are wanting; but, to make up 
for this, the embryos bear a dentary apparatus at the ante- 
rior end of the body (like that of Ascaris acus), and this might 
