464 



WORMS. 



parasitic worms. In this class the body is unsegmented, usually leaf-like in form, 

 smooth-skinned, and provided with suctorial discs in the middle or at its hinder 

 end. There is a distinct digestive canal, usually forked, but provided with only 

 one aperture, namely, the mouth. The excretory organs open by one or two pores 

 at the hinder end of the body, and, as in the tape- worms, the male and female 

 generative organs coexist in one individual. Although all are parasitic, the higher 

 members are external parasites, and develop without migration ; whereas the lower 

 ones make a complicated migration, with intermediate stages of development, 

 spending their youth in one host, and their maturity in a second. 



Many-Suckered Group, — Suborder Polystomese. 



The characteristic feature of this group is the presence in the fore-part of the 

 body of two small sucking-discs, and also of a large one and several small ones at 

 the hinder end, as well as sometimes hooks for clinging. These worms are chiefly 

 external parasites, laying fairly large eggs, and the young develop without an 

 intermediate generation. One of the best known genera is Epibdella, in which 



suckers are placed close to the true mouth, 

 giving the appearance of three apertures 

 of this nature. Fig. 1 of the illustration 

 represents a specimen of one species; in 

 the right-hand figure the head being curled 

 upwards and backwards. The posterior 

 sucker is large and furnished with three 

 hooks; the two anterior suckers are 

 smaller, and behind them is the mouth. 

 This worm is of a whitish colour, and 

 lives parasitically upon plaice and halibut. 

 Nearly related is Trochopvus, a parasite 

 of the gurnard, represented in Fig. 2 of 

 the illustration, the line to the left hand 

 of the illustration showing the natural size 

 of the animal. On the head, in addition 

 to the two suckers and mouth, are four 

 black spots, lying just in front of the last- 

 mentioned aperture, which are the eyes. 

 The posterior sucker is of enormous size, 

 and rosette or wheel-shaped; it is sup- 

 ported by nine spokes, and surrounded by 

 a fringed border. Fig. 3 of the same 

 illustration represents a species of the 

 allied genus Gyclatella, much magnified. This trematode is one of the most 

 striking members of the group. The body is oval, flat, and pure white in colour. 

 At its hinder end it is marked out by a deep notch on each side into three 

 processes, of which the. two external ones are wide and lobate, while the middle 

 one forms a slender tail-like appendage, supporting the large circular sucker. This 



TREMATODE WORMS. 



1, Epibdella ; 2, Trochojpus ; -3, Gyclatella. 



