Prof. R. Leuckart on the Development of Nenatode Worms. 331 
Pterodactyle’s place in nature appears to be side by side with 
the birds, between the reptiles and mammals, thus :— 
Mammalia 
. Aves 
XXXVIII.—On the Developmental History of the Nematode 
Worms. By Rupoiew Leuckarr*. 
THE investigations and discoveries of the last few years have in 
many respects modified our notions on the particulars of para- 
sitic life, and enriched our knowledge with a great number of 
important details. Of many parasites, even of man, we have 
now the entire life-history clearly before us. But there still 
remain many gaps in our observations; and these are nowhere 
so great and so serious as in the group of the Nematoda, or 
Roundworms. 
Our present knowledge of the life-history of these parasites 
(with the exception of the Gordiacei, which are parasitic only in 
the lower animals) is pretty nearly limited to what has been 
ascertained by Virchow, Zenker, and myself with regard to the 
Trichine. At any rate the Trichine are the only (true) Nema- 
toda whose natural history is known in all phases, and through 
all migrations. 
In the same way as the other known Entozoa, the Trichine 
live under different conditions and in different animals in their 
young and adult states. In order to arrive at sexual maturity, 
they must pass from the muscle of one bearer into the intestine 
of another ; from rats and mice they migrate into cats and pigs, 
and from the latter find their way again into their former hosts. 
That man and other mammals cccasionally come within the 
developmental cycle of the Trichine is to be regarded, in a 
helminthological point of view, as merely accidental, notwith- 
standing its fatal significance. The intercalation of these or- 
ganisms represents to a certain extent a collateral course, which 
is Just as unimportant for the circulation of the Trichine as the 
occurrence of Cysticerci in the muscles of rats or dogs in the 
life-history of the Tapeworms of man, which primarily requires 
only the interchange with the pig or the ox. 
* Translated by W.S. Dallas, F.L.S. &c., from a copy of the paper in 
the ‘ Archiv fiir Heilkunde,’ Band ii. pp. 195-235, communicated by the 
author. 
