THE SCOLEX POLYMORPHUS 823 
of this single form. He refers to these names as synonyms and 
apparently considers all the forms from whatever host to be the 
young of a single species. 
Although my experiments indicate that the 8. polymorphus of 
the Woods Hole region develops into Phoreiobothrium triloculatum 
and not into a species of Calliobothrium, a comparison of the 
larvae, as taken from the fishes about Woods Hole, with the de- 
seription which Monticelli gives shows that the two types are 
closely similar, probably almost indistinguishable. The myzo- 
rhynchus, bothria with one, two or three loculi, two faint red 
pigment spots in the neck region of some of the specimens, the 
general shape of the body and the characteristic movements, are 
apparently identical. Only in the case of the hosts they inhabit 
is there any very apparent difference, which is of course neces- 
sitated by the differences in the piscine faunas of two such widely 
separated regions. 
In his paper published in 1897, Linton suggested that the S.. 
polymorphus perhaps represents the young of a number of differ- 
ent cestodes, and also that none of the fishes (teleosts) in which 
he has found it is the true host of either larva or adult. He 
considers such larvae when found in teleosts to be ‘xencsites,’ 
or misplaced parasites, and thinks that the true intermediate 
hosts may be found among the species of crabs which frequent 
the feeding grounds of these fishes. In support of this view, he 
cites the fact that the existence of similar larvae in crustacea has 
been recorded by Van Beneden (’59). Should this hypothesis 
prove correct, we should have a case where the transfer from 
such a host to a teleost fish, while not fatal to the parasite, still 
presents conditions under which it can develop but a little way 
beyond the stage already attained. Basing his conclusion largely 
upon the presence of a median proboscis-like structure (the myzo- 
rhynchus) at the anterior end between the bothria, Linton (’97) 
expressed the opinion that our Scolex polymorphus is the young 
of the genus Echeneibothrium. This is not, however, as strong 
a clew as might seem, for in the adult Calliobothrium filicolle, 
to which Monticelli’s larvae developed, this structure is quite 
degenerate, though well marked in the larva, while in the adult 
