442 
Marine Cercariae 
free-swimming stage. The tail is slightly longer than the body, thin 
and very active. 
The full-grown cercaria measures about O'oO mm. in length, greatest 
breadth slightly less than half the length. Form of the body oval or 
more or less flask-shaped, the fore end more pointed than the hind end. 
Body covered all over with spines although they dwindle posteriorly. 
Two eye-spots conspicuous at the front end. Suckers almost the same 
size (0’06 mm. across), the oral slightly the larger. Conspicuous 
prepharynx and pharynx, short oesophagus, intestinal caeca reaching 
nearly to the posterior end of the body. Just behind the oral sucker 
are some small gland cells. Ventral sucker almost in the centre of body. 
Excretory vesicle large and pear-shaped, sometimes slightly bilobed 
anteriorly. Testes one on each side midway between ventral sucker 
and posterior end of body. Ovary in front of right testis. Sometimes 
traces of male and female ducts. 
The final host is the catfish Anarrhichas lupus and it is very 
probable that there is no intermediate host, the fish swallowing the 
Buccinum undatum with the contained rediae, the cercaria thus getting 
into the intestine without the aid of another host. I have never seen 
any trace of cysts in the catfish. 
The cercariae were found in the spring and summer, never in the 
winter. 
(c) Echinostomuin group. 
Genus Echinostomuin Rud. 
Head end provided with a crown of spines open posteriorly. 
Excretory system with much branched lateral canals. Intermediate 
host a Mollusk or in exceptional cases the cercaria may encyst in its 
first host. Final host usually a bird. 
The species of this genus are often very much alike, frequently 
possessing the same number of head spines. Three different cercariae 
are known to me all of which have 29 head spines. They can be 
quite easily distinguished however, as the rediae in which they are 
developed are quite distinctly different. I have no doubt that they 
represent different species. Moreover they are contained in constantly 
different hosts. In support of this it is to be noted that Dietz (1910, 
p. 352) recognises four species of Echinostomuin (all belonging to his 
genus Himasthla) which have 29 head spines. Odhner (1910, p. 137) 
however regards at least three of these as the same species. 
