OF THE NEMATOIDS, PARASITIC AND FBEE. 555 



as well as in the lateral, and I have seen them in the former situations only in members 

 of the genus Enoplus. 



Eberth * seems to have recognized similar structures in a species of Leptosmiatum 

 (his Phanoglene bacillata), though he put a different interpretation upon what he saw, 

 and called the structures " skin-glands " (Hautdriise). It must be admitted that the 

 recognition of their real nature is not so easy in the marine species as it is in Darylaimus 

 stagnalis. In this latter their nature scarcely admits of a doubt ; but the homology of 

 the structures to be seen in this animal with the almost similar structures which may be 

 detected in many of the marine species, as well as in the Trichosomata, is also unques- 

 tionable. I have found these channels made much more apparent after the integument 

 has been swollen somewhat, and rendered more transparent by immersion of the animals 

 in strong glycerine for about twenty-four hoursf . Although only yet detected in the 

 larger species, I suspect these pores exist in a considerable proportion of the free Nema- 

 toids. There seems to be, however, evidence to show that none such are present in the 

 representatives of the four genera Tylenchus, Cephalohus, Aphelenchus^ and Plectus. 

 Concerning the species of these genera I shall have to speak further on, and also of the 

 probable use of the integumental channels to those species in which they exist. 



In one only of the parasitic Nematoids have I seen a very close approximation to this 

 arrangement of the integumental channels, and that was in HeteraMs acuminata from 

 the frog. In this animal similar integumental pores may be seen, apparently in single 

 file, along the lateral aspects of the body (Plate XXII. fig. 12), about ■^" apart. On 

 the caudal extremity of the males these seem to be still more numerous and scattered 

 over the surface generally, in addition to the well-marked ventral suckers met with in the 

 same individuals (Plate XXII. fig. 13, c). But in the genera Trichosoma and Trichoce- 

 phalus such pores are extremely numerous, and give rise, more particularly in the species 

 of the latter genus, to an altogether exceptional appearance which has long been a puzzle 

 to anatomists ; although, on the other hand, in many species of the genus Trichosoma 

 there is a much closer resemblance to what we meet with amongst the free Nematoids. 



DuJAKDiif, describing Trichocephalus dispar, speaks of the integument as " strie trans- 

 versalement avec una bande longitudinale herissee de petites papilles." Wedl and 

 KtJCHENMEiSTER I give confusing and rather unintelligible statements concerning the 

 same structure ; but Dr. Cobbold, in his recent work ^, after alluding to these various 

 opinions as to the nature of the peculiar widening band extending along one side of the 

 body in different species of Trichocephalus, speaks in the following definite manner con- 



* Untersuch. iiber Xemat. pp. 8 «fe 19, pi. 2, fig. 1. 



t This is by far the best medium in which to mount the free Nematoids — at all events for species which are 

 not less than ~^" in length. At first they shrivel up, and the specimens appear to be ruined ; but after from 

 twenty-four to forty-eight hours the glycerine has passed into their interior, causing them to resume their 

 natural form, and making them very transparent. So mounted they undergo little change. 



X Manual of Parasites (Syd. Soc. Transl.), pp. 325, 326. 



§ Entozoa : an Introduction to the Study of Helminthology, 1864, p. 71. 



4h2 



