304 LEIDY'S DESCRIPTIONS OF DISTOMA. 



is probable these appendages served in some measure to retain the animal in its appa- 

 rently precarious position. The movements of the Distoma were rather sluggish, 

 shortening and elongating. The oral orifice frequently dilated to such an extent 

 as to make the acetabulum appear like a cup. In the contraction of the animal, the 

 intestinal rami, from their comparative shortness did not become sinuous. This 

 species belongs to the second subgenus, Dicrocodium of Dujardin, characterized by 

 " the intestine having two simple branches prolonged backward, and preceded by a 

 simple moderately long oesophagus ; anterior disk naked or without spines or lobes ; 

 ventral disk sessile ;" first section : — " testicles situated behind the ventral disk 

 before or among the folds of the oviduct."* 



It approaches most to Distoma assuIa,-\ but this has only two testes ; the posterior 

 coloring, the form of the body, and extent of the spinous appendages also differ. 



It is not more than one third or one half the size of Distoma naja.X 



Distoma vagans. D. Helicis, Proc. Acad., Vol. iii. p. 220. — Corpus album, ovale vel subrotundum, laeve, 

 sub epidermate tenui distinctissime fasciatum ; disco anteriore, subrotundo, subtus et pone apicem sito ; 

 ore duplici, apertura exteriore triangular!, interiore rotundato ; intestini ramis sinuatis } disco veutrali 

 minora, rotundato. apertura transversa, margine incrassato circumcincta. 



Long. 1-26 unc. ; lat. 1-42 unc. 



Parasiticum in Helice alternata et H. albolabre, in pericardio, etc. 



The Distoma vagans I have found in three stages of its existence in Helix alternata 

 and H. alholahris. In some one of these stages it is almost constantly found in the 

 former species of Helix. In none of them at any time can the slightest trace of 

 a generative apparatus be found, so that the animal no doubt undergoes further 

 development in some other animal. From an aperture, which is visible in the second 

 and third stages, posterior to the ventral acetabulum, I suspect the species belongs to 

 the subgenus Brachylaimus, Duj., "intestine divided immediately behind the oeso- 

 phageal bulb;" second section : — " male genital orifice behind the ventral acetabulum, 

 towards the middle of the posterior part of the body."§ 



Description of the first stage. (Fig. 13.) — Body white, oval or elongated, furnished with 

 an oval caudal appendage. Oral and ventral acetabula nearly equal, circular, l-247th 

 in. Oesophageal bulb subrotund, l-400th in. Intestine dividing immiCdiately after 

 its origin from the bulb into two very capacious and moderately tortuous branches. 

 Tail often with the appearance of an interior cup-shaped cavity ; sometimes 

 apparently perforated at the extremity ; length 1-4 00th in. 



Total length l-80th in., breadth l-123d in., but can lengthen itself to l-40th in. by 

 l-200th in. 



*DQJardin. Hist. Nat. das Helmintbes, p. 391. t Hist. Nat. des Hal., p. 398. 



t Rudolpiii Entozoorum Synopsis, p. 377, § Ibid., p. 407. 



