462 Prof. R. Leuckart on the Developmental 
The result of this experiment is so precise and convincing, 
that the above statement requires no further proof. But for 
this very reason it seems to me scarcely to be any longer doubtful 
that the Ascarides are developed in some other way, different 
from that of Trichocephalus. But if the embryos of these ani- 
mals neither escape of themselves from their shells, nor pass 
with the shells into their definitive bearer, there hardly remains 
any other course except the assumption of an intermediate host. 
But where are we to find this intermediate host ? 
I have administered the ova of Ascaris lumbricoides to a mouse 
without any result whatever. They passed out again undigested 
and with the embryos still living. I was led to make this ex- 
periment not by any hope of seeing the embryos developed into 
an intermediate form in the muscles of the mouse (for man will 
hardly introduce his roundworms by feeding on mice), but by 
the statement of Davaine that the embryos of A. lumbricoides 
fell out of their egg-capsules in great quantities in the intestines 
of the rat. It might perhaps be that the young worms only 
became capable of “development when they had passed through 
the intestine of another animal and by this means had lost their 
shells. But here, again, I got a negative result. 
The attempt to bring certain of the widely diffused lower 
animals to take up the ova of our Ascarides was equally unsuc- 
cessful. Harthworms, woodlice, and Tenebriones, which I kept 
in earth mixed with an abundance of the ova of Ascaris lumbri- 
coides, never presented these ova or their embryos when dis- 
sected. The only animal which tock them (and this was from 
water) was the Asellus aquaticus ; but it yielded them in as un- 
altered a state as the mouse. 
As, therefore, all my experiments left me just where I was 
before, I thought it necessary to strike into a new course. I put 
a number of young cats to live in a place from which I had 
repeatedly obtained animals with numerous young specimens of 
Ascaris mystax. This was a house outside the gates, with dung- 
hills and kitchen-gardens in which the animals ran about freely 
and without any particular care being taken of them. After 
residing there for six or eight days, the animals were caught 
(usually in the morning), killed, and submitted to examination. 
I had the satisfaction, in this way, not only of repeatedly de- 
tecting Ascarides of no great size (4-8 millims.), but also of 
making a discovery which, if it does not completely solve the 
question of their mode of importation, at least throws much 
light upon the destiny of our animals. 
This related to a cat about eight weeks old, which had re- 
mained for six days in the above- mentioned place. The stomach 
and small intestine of the animal had collapsed, and contained 
