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 Trochopus, 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 Cyclatella, 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 011 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 
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TREMATODE WORMS. 
1, Epibdella ; 2, Trochopus ; 3, Cyclatella. 
