26 MECZNIKOW, ON ASCARIS NIGROVENOSA. 
ments, the second of which contains a peculiar chitinous 
apparatus first described by Professor Leuckart. The intestine 
runs straight backwards, terminating in a rectum; its wall 
exhibits clear nuclei surrounded by a granular cell-substance. 
In the middle of the body is placed a largely developed 
rudimentary reproductive organ, in which may be perceived 
numerous cell-nuclei inclosing nucleoli, and which are lodged 
in a.common protoplasm. Similar cells occur in the caudal 
and in the anterior portions of the body. 
These embryos therefore are characterised especially by the 
considerable development of the rudimentary sexual organ, 
and by the double dilatation of the cesophagus—character 
which they possess in common with the free-living genus 
Diplogaster (Rhabditis), and which characters have previously 
been pointed out by Professor Heuckart as existing in the 
young larve of Dochmius trigonocephalus (I. c.). 
From the lungs, the ova, that is to say the embryos, find 
their way into the intestinal canal of the frog, collecting 
themselves for the most part in the rectum. In this situation, 
though increasing considerably in size (0°55 mm.) , they undergo 
no other changes, which do not occur until the embryos have 
been voided, and been deposited in the moist earth.* Under 
these conditions the young larvz continue to grow as before, 
and cast their skin for the first time at the end of about twelve 
hours. But it should be remarked that the length of this 
period depends very much upon the season of the year, so 
that in summer the entire development of the free larve 
requires only half the time that it does in autumn. 
After this ecdysis, individuals of two kinds may be distin- 
guished. One of these kinds presents a close similarity with 
the early larval form, from which they differ merely in their 
larger size and the rather considerable growth of the sexual 
organs. But the second kind of individuals exhibits much 
greater differences, the most striking of which consists in a 
considerable shortening and curving of the caudal extremity. 
In these individuals the rudimentary sexual organ assumes 
the form of a band, which extends as far as the rectum; 
* In water the embryos invariably perish, to which circumstance the 
miscarriage of my first experiments was due. But in order to afford the 
embryos an opportunity of further development, the contents of the 
rectum of the frog in which they were found must be mixed up with the 
moist earth, and placed in a watch-glass in a moist room, It should here 
also be remarked (as pointed out by Professor Leuckart, |. ¢., p. 227), that 
the Ascaridan larve, taken directly from the body of the parent, do not 
become completely developed ; a circumstance which would seem to indicate 
the necessity of a residence in the rectum. 
