528 THE SOCIAL LIFE OF THE LOWER ANIMALS. 
habited. We had observed, even for a long time, the parade 
worms of a fish in the intestines of certain birds; we had even 
instituted some experiments to assure ourselves of the possibility ! 
of these passages,* but all these experiments had only given a 
negative result, and the idea that transmigration was necessary 
was so completely unknown, that Bremser, the first helminthole 
gist of his age, accused Rudolphi of heresy when he stated that 
the ligules of fishes could live in birds. 3 
At a period nearer ours, our learned friend Von Siebold, called — i 
with good reason the prince of helminthology, shared more com- 
pletely this opinion, in referring the Cysticercus of the mouse to 
the Tenia of the cat, but regarding this young worm as a stray, 
sick and dropsical being. To his eyes the worm had made a: false 
journey into the mouse ; the Tænia of the cat could only live inthe — 
cat. Was Flourens romancing when I announced to the French © 
Institute that it was necessary for these cestoid worms to migrate 
from one animal to another in order to pass through the phases 
of their development ? 
At present in the zoological institute we daily repeat with the 
same success experiments on these transmigrations, and lately 
learned friend R. Leuckart, who directs with so much talent 
Institute of Leipzig, has discovered, in company with his studert 
Metznikoff, some transformations of worms accompanied with a 
change of sex; that is to say, they have seen some Nematoid 
parasites of the lungs of frogs, either always females or hermaph- 
_rodites, produce males and females which bear no resemblance © 
their mother, and whose habitual abode is not in the lungs | the 
frog, but in humid earth.+ Here we have a female, born & W 
who cannot live without aid, and who brings forth sons and d 
ters able to take care of themselves. The mother is parasitic 
viviparous, the children are, for their whole lives, free and E 
rous. 
This leads us to that other sexual peculiarity, lately onset 
of different males and females in one and the same species, 
give birth to young which do not resemble them: the same 
or rather the same species arises from two different ogg% 3 
tag ena had seen some ligules (a piip ¢ gigas see or ate 
intestines of the merganser duck. It is a = t these 
ately iher their entrance into a strange hos 
= Praca nigro-venosa, and other tte 
