102 ON THE DEVELOPMENT OF ASCARIS NIGROVENOSA. 
furnished with a vesicular nucleus 0:0048 mm. in size. In 
the immature embryo these cells exactly resemble those of 
the intestinal epithelium, their only further change consisting 
in their eventually becoming more transparent. 
With respect to the sexually mature Rhabditis-form, he 
observes that the pharyngeal walls are by no means muscular 
throughout their whole extent, as described by Herr Meczni- 
kow. Radial muscular fibres can only be noticed indwo situa- 
tions in them, viz., in the hinder enlargement, where they serve 
for the movement of the three chitinous teeth ; and more in 
front, almost in the middle of the more cylindrical cesophageal 
tube, at which point the chitinous covering is also developed 
into a sort of armature. The caudal papille also in the male 
are not hair-like, but tolerably thick and conical in form. 
The larger-sized female, which in summer usually exceeds 
1 mm. in length, has quite as distinct a nervous ring as the 
male, although this organ is by no means so distinctly de- 
fined in A. nigrovenosa as in many of the nematodes. The 
female organs are imperfectly described by Herr Mecznikow. 
They do not consist, as asserted by him, of a membraneless 
string of ova, but of two elongated sacculi, which stretch for- 
wards and: backwards from the genital opening ; and at the 
time of copulation, besides the vagina, two other divisions of 
the sexual tube may be recognised, viz., a uterus and an 
ovary. The former represents a tolerably thick, short canal, 
of narrow calibre, and apparently having cellular walls, whilst 
the ovary is formed by a very delicate, but nevertheless dis- 
tinctly demonstrable, structureless membrane ; and its interior 
is filled with ova. 
He further remarks that, although the description given by 
Herr Mecznikow of the embryos is in the main quite cor- 
rect, that observer has overlooked the interesting fact that 
these embryos, whilst they are within the emptied body of 
their parent, present the Rhabditis-form of pharynx, possess- 
ing not only the two characteristic enlargements, but also 
furnished with three chitinous teeth, smaller, it is true, than 
they are in the preceding generation, but of the same form, 
and, like them, moved by distinct muscular fibres. When 
liberated from the maternal body these teeth are lost, the 
muscular striz disappear, and the pharynx assumes a more 
Ascaridan form; the creature at the same time has become 
capable of being developed in the lungs of the frog into the 
well-known A. nigrovenosa. 
Professor Leuckart then describes experiments with respect 
to the introduction of the liberated Ascaridan embryos into 
the lungs of the frog. This experiment, it would seem, is 
