Royal Microscopical Socieiy. 211 



not the commencement of the structure known as the " Haus " I 

 am convinced, because, although I have only met with this struc- 

 ture in a fully formed condition once or twice, I have frequently 

 seen what appears to be its beginning, and in each case it was 

 separate from and covered by the hyaline substance; be that as 

 it may, all the specimens that I have examined possessed this 

 glassy covering. 



Beneath this, the body is enclosed in thick granular parietes, 

 which extend from each side of the generative gland forward to the 

 entrance of the pharynx ; the deficiency of this granular wall at the 

 posterior end of the body is filled up by a thin membrane, to 

 which the generating gland adheres. The interior of the parietes is 

 lined by what appears to be an epithelial layer, which presents the 

 appearance of variously shaped cells at different portions of the 

 body, but I am not decided whether this layer is a separate 

 structure, or whether it is only the optical expression of the 

 elements composing the thickened parietes, for when an optical 

 section of the wall is obtained a distinct and separate layer of 

 epithelium cannot be made out ; surrounding the entrance to the 

 pharynx, however, these quasi cells have a four-sided appearance ; 

 as seen from the haemal side there are four rows of them, here 

 they approach the form of a square ; but on the neural side they 

 resemble layers of bricks, each element forming a parallelogram 

 with the angles rounded ; behind these, in that part of the walls 

 covering the endostyle on the haemal side and the nervous 

 ganglion on the neural side, they are circular in outline, being 

 arranged in rows in such a manner that those of the second row 

 occur opposite the interspaces of the first row, those of the third in 

 like manner opposite the interspaces of the second, and so on. In 

 some few cases these cells appear to be hexagonal in shape ; when 

 this occurs each hexagon is separated from its neighbour by a clear 

 line when the focus is properly adjusted. 



As soon as the process of dying begins to set in, these cell-like 

 appearances are more distinct, the divisions between them become 

 more marked, they swell out, and on a profile view project as 

 rounded eminences into the somatic cavity ; it is this appearance 

 which perhaps gave Dr. Fol* the idea that the somatic parietes 

 were composed of a single cellular layer, which he terms the 

 ectothelium or epidermis ; but in healthy specimens the walls of the 

 body, as seen in an optical section, present only the appearance of 

 indistinct molecules imbedded in a granular substance, with the 

 above-mentioned cells forming an apparent lining membrane. 



Belonging to the integumentary system is a large gland, which 

 Dr. Fol declares to secrete the gelatinous material forming the 

 so-called " Haus," which interpretation I am inclined to confirm 



* Loc. cit. 



Q 2 



