OF THE NEMATOIDS, PAEASITIC AND FREE. 557 



clearly perceived. When the mouth of the channel is looked down upon, and brought 

 into focus at the surface of the integument (where it corresponds with a minute 

 depression), it appears as a bright circular space about ysoWu" ^^ diameter; and as 

 the focus is lowered a dark roundish or polygonal halo is developed around it, giving 

 rise to an appearance which led Dr. Cobbold to speak of epidermal cells with clear 

 central spaces. This dark border I believe to be due simply to an alteration in the 

 diifraction of light by the bounding walls of the integumental channel, and the upper 

 extremity of the columnar cells beneath coming into focus as the object-glass is lowered. 

 In the TrichocepJiali, only one such band exists in the dorsal aspect of the anterior part 

 of the body ; but in the various species of the genus Trichosoma more commonly two 

 exist, which may be either dorsal and ventral, or lateral *. In the members of this 

 genus the pores are frequently not nearly so numerous, and in Trichosoma longicolle at 

 least (the only specimen that I have examined), both these and the cellular bands 

 beneath seem to approximate very closely to what we meet with in the free Nematoids 

 (Plate XXVII. fig. 14) ; and in which also, as just stated, we see the same variation as 

 regards the situation of the integumental channels. 



Yet other openings through the integument remain to be spoken of, which, so far as 

 I have observed, exist only in the parasitic species, and of these never in the Tricho- 

 cephali, Trichosomata, or Heterakis acuminata. I allude to two lateral openings, of a 

 much larger kind than those previously described, situated one on each side of some 

 portion of the oesophageal region of the body, and two posterior latero-ventral openings, 

 of the same character, between the anus and the posterior extremity of the animal f . 

 These structures have been observed both by Schneider and Eberth ; by the former 

 they have been described respectively as "cervical and caudal papillae";};, and by the 

 latter as openings of the water-vascular system §. In many of the Nematoids in which 

 they are met with, these structures do present such an appearance as to lend support to 

 Dr. Schneider's view as to their natui-e, inasmuch as they are almost identical in their 

 structure with the ventral papillae of male Ascarides, consisting generally of a conical 

 projection of the deep layer of integument into the inner part of the chitinous layer, 

 where it is in connexion with a distinct channel through this substance opening in the 

 centre of a sui"face-depression. But in Ascaris lumbricoides, the animal in which, quite 

 independently, I first recognized these openrags, the anterior channels through the 

 integument are altogether so marked and well developed in proportion to the granular 

 projection (Plate XXII. figs. 14 & 16), that from the first I looked upon the integu- 



* Ebeeth, Untersuch. iiber Nemat. Taf. vi. u. vii. 



t Two similar lateral openings are spoken of by Ebeeth in Sjoiroptera undnata as existing near the middle 

 of the body, posterior to the vagina. I have seen such median openings also in one species, but having made 

 no note of it at the time, cannot be quite sure as to the animal in which they were seen — I think, however, it 

 was in Strongijliis filaria. 



X Neue Beit, zur Anat. und Morph. der Nematoden, Reich, and Du Bois-Retm. Archiv, 1863, p. 15. 



§ Wurtzb. Naturwiss. Zeitsch. 1860. Erst. Bd. Taf. ii. 3 a, u. Taf. iii. 13 a; Untersuch. iiber Nemat. 

 Taf. \iii. u. is. 



