NEW LARVAL TREMATODES. 769 



large cells situated in a transverse row immediately in front of 

 the ventral sucker. There are two pairs, a right and a left. The 

 ducts from each pair unite almost at once, and the united ducts 

 then pass foi'wai-d in an irregular course ; but just before they 

 reach the oi-al sucker each makes a characteristic twist, following 

 which there is a gradual increase in calibre until near the termi- 

 nation, when they contract slightly again. The cystogenous 

 glands have an irregular rectangular outline, and measure 

 •048 X "037 mm. In direct contact with the oral sucker is the 

 small muscular pharynx measuring -024 mm., which is continued 

 by a short, somewhat dilated oesophagus of the same length as 

 the pharynx. The intestinal bifurcation is about midway between 

 the two suckers. The diverticula are simple, somewhat wide 

 tubes, which terminate not far behind the ventral sucker (i. e. a 

 third of the distance from the sucker to the posterior end of the 

 body). The excretory vesicle is Y-shaped. A common trunk is 

 practically absent, and the limbs extend forward to near the 

 terminations of the intestinal diverticula. The excretory tubules 

 are very fine ; the main tube on each side extends forward to 

 near the oral sucker, where it turns back. The excretory aj^erture 

 appeai^s to be slightly dorsal. 



No trace of other organs could be made out, so that no accurate 

 idea can be obtained of the systematic position of this larva. 

 The peculiar configuration of the excretory vesicle may, in con- 

 junction with the shape of the alimentary canal, eventually lead 

 to the identification of its adult form, but at present, so far as I 

 am aware, there is no known adult Distome to which this larva 

 can be ascribed. 



The second form, which I name Diplostomum sirtale, sp. n. 

 (text-fig. 107 b), differs markedly from the first. It is about the 

 same size, and occurs in somewhat similar cysts, but its shape and 

 colour are entirely different. The body of Cercaria ordinata is 

 light and transparent, whereas that of Diplostomum sirtale is 

 dark and almost opaque. The opacity is due to the presence of 

 innumerable small granules distributed throughout the whole 

 body. The shape is that of a typical Biplostoimcm larva, being 

 scoop-like with a short handle. The shape is due to the rollino- 

 over of the postero-lateral margins of the body. In life, however 

 these margins are capable of more or less eversion, so that on 

 occasion the body may appear almost flat. The dimensions of 

 this larva are •48--55 x •28-'32 mm., the short stumpy tail beino- 

 •06 mm. long. 



The oral sucker measures •OS 9 mm. in diameter ; the ventral 

 sucker •042-^045 mm. The latter is situated a little in front 

 of the middle of the body, •25--28 mm. from the anterior end. 

 Midway between it and the posterior end of the body occurs 

 the characteristic Holostomid fixing disc, which appears as 

 a transparent disc about the same size as the ventral sucker. 

 Of the internal organs only the alimentary canal and excretory 

 vesicle were visible. The former comprises a pharynx contiguous 



