368 
Tetrarhynclius erinaceus 
degenerate and the cysts contained only calcareous corpuscles with 
some obscure connective tissue. This may also be the case with the 
cysts found on the mesenteries or peritoneum. 
I have not, in the meantime, any observations to record with 
reference to the life-history of Tetrarhynchus erinaceus. The scheme 
usually adopted is that given by Braun (1894-1900, p. 1609) and this 
is purely conjectural. The identification of Trigla as the larval host is 
based solely on the recognition of the scolex of the Plerocercoid larva as 
that of T. erinaceus. As to this identification there is very much doubt: 
there is no doubt, of course, that the larva inhabiting the cysts found in 
Trigla is really that of T. erinaceus, but it is far from being certain that 
the Rays are infected by eating species of Trigla and other Teleost fishes 
containing these Plerocercoid larvae. In order to prove that Trigla, or 
Gadus merlangus, or any other of the Teleostean fishes mentioned above 
are really larval hosts in the proper sense we should have to show (1) 
that they are themselves infected by eating proglottides voided by the 
Ray, or that they eat some invertebrate, which is infected by eating the 
proglottides; (2) and that the Ray becomes infected by eating Trigla 
or any other Teleost fish containing the Plerocercoids. Now there is no 
evidence whatever that these things happen, and no feeding experiments 
have been made with the object of establishing the life-history. The 
eggs of the worm develop within the uterus but I have never seen the 
six-hooked larva in this situation. Possibly further development may 
occur after the dehiscence of the mature proglottis from the parent 
strobila, while the former is still within the intestine of the Ray, or even 
while it is lying on the sea bottom after having been passed by the fish. 
Now the free proglottis is only about 0'5 cm. in length and it is very 
unlikely that such a small object should be eaten by fish like Gurnards, 
Whiting, etc., which habitually feed on much larger organisms. It is, of 
course, quite possible that even such small objects may be eaten by 
the fishes accidentally, but the infection of the so-called larval hosts is 
so general that we can hardly suppose the 23rocess to be a matter of 
accident. I think it is far more likely that the ripe proglottides are 
eaten by some small invertebrate, a crustacean or mollusc or small fish, 
and that the latter is then eaten by the so-called larval host. 
It is highly unlikely that the Ray is infected by eating such fishes 
as Gurnards or Whiting containing the Plerocercoid larva. Ray usually 
eat Crustacea and quite small fish, and the assumption that they receive 
the tapeworm from a Teleost fish is not supported by an examination of 
their food. It is more jDrobable then, that the adult host is infected by 
