TREMATODES FROM FISHES — LINTON 111 



Hirudinella clavata (Meuzies), Coopeb, Trans. Roy. Soc, Canada, ser. 3, vol. 9, 



p. 1S6 (from Thunnus thynnus), 1915. 

 Hirudinella ftisca (Poirier, 1SS5), Manteb, Illinois Biol. Mon., vol. 10, no. 2, pp. 



101-107, ligs. 7&-79 (from Xiphias gladius), 1926. 



Large distomes belonging to the group represented by Distonrmm 

 clavatum Eudolphi are here considered. The anatomy of these dis- 

 tomes, so far as it is shown by sectioned material from the swordfish, 

 horse mackerel, and cutlassfish, is in general agreement with Manter's 

 excellent description of H. fusca (Poirier) from the swordfish. 



Externally the distomes from the swordfish exhibit some fairly 

 constant differences from those of the horse mackerel. Thus, in dis- 

 tomes from the swordfish, the neck in alcoholic specimens is usually 

 arched and slender, the body somewhat elongated, increasing in 

 diameter from the ventral sucker toward the posterior end, then 

 tapering quickly and rather coarsely wrinkled (fig. 134). In dis- 

 tomes from the horse mackerel the neck is very short, conical, and 

 reflected dorsally ; body, in most cases, cylindrical and crossed by fine 

 wrinkles (fig. 135). Forms more or less intermediate, however, occur 

 among the distomes from each host. 



These distomes agree in having the opening of the metraterm 

 behind the genital papilla. The latter is a very muscular structure 

 and in some cases was found to be protruding from the genital pore 

 (fig. 138). A large prostate accompanies the more or less coiled or 

 folded ejaculatory duct, and is followed posteriorly by the seminal 

 vesicle, which is also more or less coiled or folded. The two testes 

 are close to the posterior border of the ventral sucker, close together, 

 and diagonally placed. The ovary is immediately behind the testes, 

 and the shell gland is posterior and ventral to the ovary. The 

 tubular vitellaria and folds of the uterus extend from the ventral 

 sucker about halfway to the posterior end of the body. An interpre- 

 tation of the genital ducts, associated with the shell gland, as shown 

 in serial sections of a distome from the swordfish, is given in figures 

 151-153. Laurer's canal approaches the shell gland at its anterodorsal 

 border near the ovary. It enlarges to form a relatively small seminal 

 receptacle, which has the appearance of being divided into five or six 

 compartments. This may represent the more or less coiled portion 

 of the empty canal observed in sections of the distome from the cut- 

 lassfish (fig. 150). This observation was made on a series of frontal 

 sections of a distome which had been flattened at the time of fixation. 

 Laurer's canal, in this series of sections, in its course to the dorsal 

 surface, lies near the posterior border of the second testis. 



Structures from the subcuticular layer penetrate the cuticle (fig. 

 155). In one series of sections the cuticle was partly macerated and 

 presented the appearance of being finely papillate, or spinose. 



Additional details given in notes under the several hosts. 



