566 DE. H. CHARLTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



ceming this, as met with in T. affirm : — " According to my own obsenations this ban3 

 is a genuine structure, and is made up of projecting, bluntly-pointed, polygonal epider- 

 mal cells, which in certain adjustments of the focus refract transmitted light so strongly 

 that the band looks as if it consisted of a regularly arranged series of pigment spots 

 (fig. 3, a); at other times the centre of each cell becomes clear (a), and the irregular 

 polygonal character of each individual cell is rendered more apparent." Dr. Eberth 

 seems to have examined most carefully many species of the genera TricliocepTialus and 

 Trichosoma, and has also expressed very concise opinions concerning these bands of 

 which we have been speaking. According to him *, these appearances are caused by 

 solid staff-like prolongations into the substance of the skin, given off from and situated 

 upon certain closely-packed, cylindrical, or elongated-polygonal cells, — the whole struc- 

 ture representing a variety of the dorsal median line as it exists in these Nematoids. 

 He seems to think that the prolongations are developments from the cell-wall, and is 

 decidedly of opinion that they are solid. 



After the most careful examination of Trichocephalus dispar, T. affinis, and Tricho- 

 soma longicolle, I am unable to agree with any of these observers. 



More than twelve months ago, before knowing anything of Eberth's obsen'ations 

 (which do agree in some respects wdth my own), I was enabled to discover what I 

 believe to be the real nature of these structures, during the examination of a specimen 

 of Trichocephalus dispar, whose integument had been rendered more transparent by 

 boiling the animal for two or three minutes in dilute acetic acid. Certainly there are 

 no actual elevations of the integument into " papillae " in the region of the band f , though 

 the transverse markings decidedly cease at its borders (Plate XXVII. figs. 15 & 17); 

 neither are there any " epidermal cells," as described by Dr. Cobbold, and indeed their 

 presence is quite irreconcileable with the chitinous nature of the epidermis in the 

 Nematoids generally : both these appearances are, I believe, purely optical delusions, 

 owing to errors of interpretation. I differ from Eberth with respect to the description 

 he gives of this band in one point only, though that is a most important one. What 

 he considers as solid staff-shaped prolongations I believe to be integumental channels, 

 essentially similar to those which I have previously described as so common in the free 

 Nematoids. This would scarcely be imagined from an examination of the band through- 

 out the greater part of its extent ; but its posterior tennination is by no means abrupt, 

 and in that region its constituent elements are scattered widely apart and are quite 

 isolated from one another before they entirely disappear on the thicker portion of the 

 body. An examination of this region permits these integumental channels to be seen 

 under different aspects (Plate XXVII. fig. 16), and enables their real nature to be more 



* Untersuch. iiber Nemat. 1863, p. 46. 



t Unless we so term, with DirjAKDiir, certain larger rounded prominences of the integument often seen 

 bounding the band in some portions of its length — "papilles plus grosses qui se gonflent par endosmose." 

 These are altogether unimportant structures, due simply to a partial separation (such as we may often meet 

 -with in the Nematoids) of the most superficial lamella of the epidermis from that beneath it. 



