History of the Nematode Worms. 463 
no chyle; but the former contained a few bitten fragments of 
straw and all sorts of vegetable débris, among which a micro- 
scopic investigation distinctly showed fragments of potatoes and 
of potato-parings. 
But the same stomach contained also at least forty to sixty 
Nematode embryos, some of which measured only 0°4—0°6 mil- 
lim. ; so that the smallest individuals were scarcely larger than 
the embryos of Ascaris mystax while still enclosed in their egg- 
capsules. However, there could not be the least doubt that the 
embryos which I found here free and twisting about briskly on 
the mucous membrane of the stomach of the young cat were 
those of Ascaris mystax. Not only did they, especially the 
smallest specimens, agree exactly with the animals from the eggs 
with which I was so well acquainted, but I could also follow 
them through all stages of development up to young Ascarides 
of 3-4 millims. in length, which occurred, together with the 
larger embryos, in the small intestine, and, notwithstanding 
their small size and slender form, already presented precisely 
the characters of the Ascaris mystax of the cat. 
In the first place it was proved by this discovery that Ascaris 
mystax (and also decidedly the other allied Ascarides, including 
therefore A. lumbricoides) retains its original developmental 
condition up to the time of its introduction into its definitive 
host, or, in other words, immigrates into its definitive bearer in 
the embryonic form. In this respect A. mystax therefore behaves 
like the above-mentioned A. acus; nay, it even surpasses the 
latter, as before its transfer to its definitive habitat it does not 
even increase in size. 
But what the embryos previously wanted is made up imme- 
diately after their immigration. The embryos grow, without, 
however, essentially altering their structure ; they grow rapidly, 
and pass, when about 1:5—2 millims. in length, from the stomach 
into the small intestine. The intestinal cells gradually acquire 
a brownish colour during the increase of size. The muscular 
sac is thickened, and the glandular stomach gradually separates 
from the posterior extremity of the cesophagus as a special struc- 
ture. But the rudimentary sexual organ still remains without 
any further development, and the mouth still bears the embry- 
onic boring-tooth instead of the three lips. These conditions 
are altered only when the next change of skin takes place, at a 
length of 2°8 millims. A little while before this, the genuine 
structure of the Ascaride mouth may be distinguished under the 
cuticle of the head; and the increase of the genital rudiment 
into a short sac, either simple or Y-shaped, according to the 
sex, may be observed. The formation of the spicula only takes 
place subsequently, when the worm has already attained a length 
