VI 



PHYLUM NEMATHELMINTHES 



307 



CLASS II. ACANTHOCEPHALA. 



This class contains a number of genera of parasitic worms, of which 

 Echinorhynchus is the chief. The present section will be devoted to this genus, 

 a not uncommon parasite in the intestine of Mammals, Birds, Reptiles, 

 Amphibians, and Fishes. The largest species, E. (Gigantorhynchus) gigas, is 

 found in the Pig (Fig. 254, A), and has once been recorded in the human 

 subject : it may attain, in the female, a length of 50 cm., or more than half a 

 yard. Most species are small, not exceeding 1 cm. in length. 



External Characters. The body is cylindrical, and ends in front in a 

 protrusible portion, the proboscis (A, p., B, pr.), which is cylindrical and is 

 covered with many rows of recurved chitinoid hooks. The worm lies with the 

 proboscis sunk in the wall of the intestine of its host, which is sometimes 

 riddled with holes formed in this way. In some species there is a distinct 

 neck (B, .) between the proboscis and the trunk, and there may be a globular 

 dilatation at the anterior end of the neck. At the hinder end of the body is 

 a single aperture, the gonopore or reproductive aperture (gnp,) : connected 



jbr 





If 



FIG. 254. A, Echinorhynchus (Gigantprhynchus) 

 gigas, female, from the Pig (nat. size); B, E. 

 lesiniformis, male, from the edible Frog (magni- 

 fied), b. bursa ; c. gl. cement glands ; gnp. gonopore ; 

 Im. lemnisci ; n. neck ; p. or pr. proboscis ; r. m. 

 retractor muscle of proboscis ; s. Ig. suspensory liga- 

 ment ; ts. testis ; v. vessel. 



with this, in the male, is a protrusible, bell-like structure, the bursa (b.}, which 

 acts as a copula tory organ, like the somewhat similar organ in certain Nema- 

 toda. There is no trace of mouth, anus, or excretory pore. 



The body-wall is covered with a stout cuticle, beneath which is a striated 

 protoplasmic layer, probably representing the ectoderm. Then comes a layer 

 of transverse, and then one of longitudinal muscles. The body-wall thus 

 constituted encloses a spacious body-cavity or coelome containing a clear 



X 2 



