28 MECZNIKOW, ON ASCARIS NIGROVENOSA. 
The female differs from the male chiefly in in its longer 
and slenderer tail. The excretory orifice is present as in the 
male; but it is otherwise as regards the nervous system, 
which in the female appears to consist simply of an aggrega- 
tion of undifferentiated cells. 
The fully developed female possesses a plumper form than 
the male, its length not being more than twelve times its 
diameter. During the growth of the ova, that is to say, of 
the embryos, the female continues to increase in thickness. 
In length it generally exceeds the male, but differences in 
this respect may be observed. Whilst some individuals may 
be seen 113mm. in length, others will be found barely 
0°65 mm. long. 
The vagina is situated in the middle of the body ; it leads 
into the double reproductive organs, which are of extremely 
simple structure. They consist merely of contiguous cells, 
which are developed into ova, of which only those which lie 
nearest the sexual orifice complete their development. In 
the female reproductive organs I have been unable to detect 
any special walls, whose existence has been affirmed by Pro- 
fessor Leuckart (l.c., p. 228). And the impregnated ova 
also are equally without any membranous covering. 
The embryonic development of the new generation goes on 
in the interior of the free-living female, and presents nothing 
worthy of remark;,, The new embryos, which are not enclosed 
in any special sac; and are developed to the number of from 
one to four, straighten themselves out soon after their com- 
pletion, and exhibit spontaneous movements in the interior of 
the maternal body. Atthe same time they begin to devour the 
undeveloped ova, as well as to prey upon the internal organs 
of the mother, in consequence of which they grow very ra- 
pidly. At the end of a few hours nothing remains of the 
maternal body except the cuticle, within which the actively 
moving embryos may be perceived, surrounded with nume- 
rous opaque granules. 
On the fifth day after the exit of the young larve of As- 
caris nigrovenosa from the rectum of the frog, the embryos 
of the new generation just described are ready to quit the 
cuticle of their devoured parent. These new larve, about 
0°65 mm. long, differ from their parents in their lively move- 
ments and far slenderer form, the proportion of their length 
to the diameter being as 25 tol. ‘Their cuticle exhibits dis- 
tinct, sharply defined longitudinal strize. The minute oral 
orifice leads into the cesophagus, which for some time, as in 
‘the parents, is furnished with two dilatations; but subse- 
quently this conformation disappears, when the cesophagus 
