60 COITTRIBUTIONS TO AMERICAN HELMINTHOLOGY. 



5. — DiSTOMXJM GRACiLE. Dicsing. 

 Clinostomum GRACILE. Leidy. 



This worm was first described by Dr. Leidy, ^^ wlio regarded it as 

 generically different from Distomum. He records it from tlie in- 

 testines of a Pike, and from cysts in the gUls, fins and muscles of 

 Pomotis vulgaris (auritus), Giinther. I have found the same worm 

 in cysts on the branchiostegal membrane and anterior fins of Perca 

 flavescens, Cuv. This species appears to me to belong to the same 

 group as D. heterostomum and D. dimorphum, from the structure of 

 the anterior end, and of the ventral sucker. In a specimen of 6.45 

 mm. in length, with a greatest breadth of 1.8 mm. across, the mouth 

 sucker measures 0.338 mm. across, and the prominent border which 

 surrounds it 0.975 mm. The large ventral sucker (0.91 mm.) is situ- 

 ated in the middle of a constriction dividing the neck from the 

 body, and has a triangular aperture. Its cavity is lessened by three 

 triangular tongues, which project into it so as nearly to meet each 

 other. The anterior of these points with its apex backwards ; all 

 are formed chiefly of radial fibres, and they must undoubtedly 

 increase the efiiciency of the sucking apparatus very considerably. 



The species of Distomum which have been found included in cysts 

 are either fully mature (D. agamos, Y. Linst.," D. Okenii, Koll., 

 D. crassicolle, E.. [Pontallie] ), or have only one part of the sexual 

 apparatus ripe (D. hystrix., Dujard., the testes^^), or are finally quite 

 immature. In the last category fall D. annuligerum, Nordm., D. 

 diifusocalciferum, Gastaldi, D. dimorphum, Diesing, and, as I believe, 

 D. gracile. No mention of generative organs is made in Leidy's 

 description, and I have failed to detect any trace of such. The Sun- 

 fish and Perch can consequently hardly be regarded as the definitive 

 hosts of this worm. Probably the sexually mature worm is to be 

 sought for in the intestine of some larger fish (Pike?) or piscivorous 

 bird. In the latter case, the relationship between the immature 

 and mature form would resemble the two forms of D. dimorphum 

 described by Diesing. 



The intestiaal coeca are large, and extend nearly to the posterior 

 end; the contents are yellowish-brown, and include some lozenge- 

 shaped concretions. 



w Proo. Ac. Sci. PhU. VIII., p. 45. 



i^ Trosch. Arch. XXXVIII., B. I., p. 1, f. 



18 Olsson, Lund's Univers. Arsskr. IV., p. &2. 



