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yellowish colour, the enclosed cercarise being colourless. The 
intestine of the redia gradually diminishes, and is pushed out of 
position by the foremost cercaria. 
The cercaria (figs. 7-8) may be tailed or tail-less. In the first 
infected specimens of Buccinum undatum examined, all had tails 
and moved about actively by aid of these, but in the later specimens 
very few had tails, and these when present seemed to be of little use. 
Tailed and tail-less forms occur in the same redia. By far the 
greater number have no tails, and all move by creeping in a leech - 
like manner by aid of their suckers. It remains to be seen whether 
a tailed stage precedes the tail-less one in the redia. The tail when 
present is thin and longer than the body. It is very easily detached. 
The interesting fact that the tail may be either present or absent 
shows that it is not a necessary organ, and this is borne out by the 
supposition that the Catfish eats the Buccinum, and the cercaria 
becomes a mature worm without entering an intermediate host and 
without a resting stage. We, therefore, see this apparently useless 
organ disappearing, in some cases entirely. 
The absence of large glands which are often present in otheir 
cercaria), and serve to secrete the cyst, bears out the theory that the 
present worm omits the encysted stage. From the number of 
specimens present in the Catfish, it is extremely likely that the 
worm enters directly from the Buccinum. 
The usual length of the cercaria in live pressure preparations 
is 050 mm., in preserved specimens they contract considerably, 
and measure only about 035 mm. The greatest breadth is less 
than half the length. It is difficult to say what is the shape of 
the cercaria as it is so contractile that its shape is continually 
changing. It is certainly never so flask-shaped as the adult worm, 
and there is not much difference in the shape of the head and tail 
ends. The body is covered with spines which dwindle posteriorly, 
but are never absent. The eye-spots are conspicuous. The 
suckers almost the same size (0-06 mm. across), but the oral may 
be slightly larger. The prepharynx, pharynx, and intestine agree 
with those of the adult worm. The excretory vesicle is large, and 
sometimes appears bilobed. The testes are symmetrically placed, 
one on each side about midway between the ventral sucker and the 
posterior end of the body. The ovary may in some specimens be 
seen in front of the right testis, and there are sometimes traces of 
the male and female duct. Just behind the oral sucker is a little 
row of gland cells of a pale yellowish colour. 
