History of the Nematode Worms. 461 
clear and too accordant to permit one any longer to imagine an 
infection of this kind. If we had to do with matters of rare occur- 
rence, we might certainly at least suppose that the circumstances 
of the experiment had not fulfilled the conditions necessary for 
the development of the parasites; but the worms in question 
are, as is well known, so abundant, that this objection can 
hardly be maintained. 
That, however, there are really Nematoda which migrate 
directly into their definitive host by the medium of ova containing 
embryos, in the manner here indicated, is indubitable, from the 
results of other experiments made by me. ‘The proof of such a 
development was most strikingly obtained in the case of Tricho- 
cephalus affinis of the sheep, the destiny of which, considering 
the perfect agreement of the ova and embryos, must be regarded 
as furnishing a rule for the 7. dispar of man. 
The embryos of this animal have already been mentioned as 
short plump worms, of 0:127 millim. They have a thick and a 
thin end, and terminal orifices to the alimentary canal, like the 
embryos of Trichina, but unlike those of all other Nematoda. 
They also resemble the embryos of Trichina in the fact that their 
organization exhibits but little differentiation. Their movements 
consist of very slow changes of position within the egg, during 
which the thicker end of the body is usually pushed in advance. 
My material for experiment consisted of the whole of the ova 
of some twenty female individuals, which had been kept for 
about seven months in water, and had been completely decom- 
posed therein. Sixteen days after administration, the experi- 
mental animal (a young lamb) was killed. To the naked eye 
the large intestine presented nothing unusual, but the micro- 
scope immediately revealed upon it many hundreds of young 
Trichocephali. The majority of these worms measured about 
0-8-1 millim. ; but there were specimens of only 0°5, and others 
of nearly 2 (one even of 2°4) millims. in length. Leaving out 
of consideration the absence of sexual development, they pre- 
sented exactly the aspect of the intestinal Trichine. They were 
clear capilliform filaments (0-024 millim. thick), which, notwith- 
standing the presence of a diminished anterior end, showed as 
yet no indication of the characteristic ultimate form. In the 
interior, besides the cellular body, which traversed nearly the 
whole cavity of the body, the cesophagus and the short chyle- 
stomach were to be distinguished, the latter with a muscular 
terminal piece which, in the larger specimens (in the males), 
was not unfrequently clearly divided from the true stomach in 
the form of a distinct section. In the larger worms the genital 
tube could already be distinguished, running down beside the 
chyle-stomach. 
