350 ANIMAL PAEASITES. 



animals experimented on, as might have been expected from 

 Herbst's experiments. 



It now remains for me again to sum up the reasons which 

 determine me to regard the Trichina of Owen and Luschka, and, 

 I repeat, only this species, for the young brood of Trichocephalus 

 dispar, and both these nematode worms, hitherto placed 

 separately, as belonging to one species. 



1. As regards the skin, both Trichocephalus dispar and 

 Trichina spiralis have a peculiar "ringed and jointed structure, 

 which presents itself more distinctly than in many other 

 Nematoda. 



2. In both a longitudinal stria runs down the sides, indicating 

 the limit to which the contractile parenchyma of the worm, in 

 which its internal organs are imbedded, reaches. Above these 

 striae we only meet with the layers of the skin free from all 

 parenchyma. These striae are certainly at the same time the 

 points of attachment of the parenchyma to the inner wall of the 

 integument of the Trichina. 



3. The alimentary canal is organized in exactly the same way 

 in both. Thus in the first place the mouth and anus are 

 situated exactly in the centre of the two extremities of the body, 

 the anterior and posterior. Even this simple circumstance 

 excluded the whole of the Ascarides, Oxyurides, and Strongyli, 

 and a great number of Filarice, from any relationship with 

 the Trichina spiralis of Owen and Luschka. Of the Nematoda 

 occurring in the human subject, the Trichosoma and Trichocephali, 

 from their form, still remained for comparison. The Trichosoma 

 are distinguished by the extraordinary thinness of their bodies 

 and the scarcely perceptible increase of the circumference of the 

 animal at the abdomen, whilst the Trichocephali and Trichinae 

 have a distinctly acuminate, thin anterior end, and a thicker, 

 blunt posterior extremity. It was this circumstance that first 

 led me to suspect the identity of the two latter worms, and we 

 shall see that the further comparison only lends new support to 

 this identity. In Trichocephalus dispar and in the Trichina 

 spiralis of Owen and Luschka, there is at the thin anterior 

 extremity of the body a small, globular, button-shaped structure, 

 capable of being protruded from and retracted within the mouth, 

 which is wanting in other Nematoda. Immediately after this 

 mouth follows a spiral-like portion of intestine (commencement of 



