ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 233 



external form, the description of the integument is entered upon, and 

 it is pointed out that if we look upon the tegumentary layer of the 

 Trematodes as having the same structure as that ordinarily described 

 as obtaining in the Cestoda, we must regard the parenchymatous-like 

 cellular layer which succeeds the muscular as being of an epithelial 

 nature, for its fine processes pass out between the muscular fibres, 

 fuse above it, and secrete the " cuticle " ; if this view of the nature of 

 the parts be the correct one, it is clear that all that has been said 

 about the presence of nuclei in the cuticle must rest on erroneous 

 observations. 



The movement of the body of Gasterostomum is described as being 

 effected in the following fashion : the body is narrowed and elongated 

 by the contraction of the circular muscles, the head is then protruded, 

 the sucker widens and deepens, and at the same time the muscles in 

 the upper lip of the sucker, aided by others, bring about a flattening 

 of the anterior surface of the body and the formation of a dorsal ridge 

 by the aid of which the body fixes itself ; by the contraction of the 

 longitudinal muscles the body is drawn after the sucker. 



In both Bucephalus and Gasterostomum it was impossible to detect 

 the limits of the cells of the parenchyma, but in the latter they were 

 clearly seen to be of two forms ; some elongated or branched, which 

 were of a connective or muscular nature, and others rounded and less 

 coloured, which seemed to take a part in the osmotic distribution of the 

 nutrient material. The nervous system is briefly described. 



In Bucephalus we find at the last third of the body a small tubular 

 depression of the integument, which leads into the pharynx ; this can 

 suck in fluid by enlarging and then undergoing a peristaltic contraction. 

 The oesophagus is formed by a homogeneous layer. In the intestine 

 there are large yellowish cells ; if the animal has been for a long time 

 in water the intestine is found to have fluid contents in which float green- 

 ish yellow spherical concretions. The intestine may seem to be pro- 

 duced into two processes, which appear to owe their origin to the 

 compression, on the ventral wall of the body, of the ventral sucker. 



The arrangement of the muscles of the pharynx is the same in 

 Bucephalus as in Gasterostomum ; in the latter the stomach has an oval 

 contour, while the intestine has in form, position, and structure a con- 

 siderable resemblance to that of the Ehabdocoelida. The author is 

 the first who has detected the presence of a distinct oesophagus in 

 Gasterostomum. 



The quantity of water which passes through the water-vascular 

 system of Bucephalus is so great that it may well be supposed to have 

 a respiratory as well as an excretory function. 



In Bucephalus, cells with nuclei which colour intensely, are to be 

 seen in the last fourth of the body ; these are probably converted into 

 the penial sheath ; somewhat more anteriorly and dorsally there are 

 several groups of closely appressed cells, the nuclei of which are very 

 intensely coloured ; these are supposed to be the indifierent rudiments 

 of the reproductory elements. The generative apparatus of Gastero- 

 stomum is described, and a hypothetical account of the mode of action 

 of the copulatory organ is given. By the action of the longitudinal 



Ser. 2.— Vol. IV. K 



