1138 The American Naturalist. [December, 
inland again. During these calm hours in the morning all the more 
important.collecting was done. 
The larva is undoubtedly a free-swimming stage of one of the marine 
Trematodes. Such pelagic larve—Cercaria—are not unknown, 
but have been now and then recorded by naturalists. ‘The adult 
worms generally live, believe, in marine molluscs, and the 
Cercaria is a larval form seeking a new host. The larva belougs 
to that. division of marine larval Cercaria having bifid tails. Villot 
says that these Cercaria having split tails form a small very 
natural group, and are mostly 
_ found parisitic in fresh-water 
Mollusca; but a few are marine. 
One of these has been recorded 
by J. Miiller as having been 
found near Nice, and has been 
figured in the inaugural thesis of 
Lavalette Saint-George, under 
the name of Cercaria dichotoma. 
I have not seen this figure, but 
judging from the account of the 
same larva given later by Cla- 
parede it is entirely different 
from the Jamaica larva. 
Claparede, in 1863, figured a 
bifid-tailed Cercaria found in the 
sea. This is also quite different 
from the Jamaica Cercaria. The 
larva figured by Claparede is called Bucephalus haimeanus, and is very 
close, the author says, to B. polymorphus, described by Von Baer, and 
is the same as that described by Lacaze Duthier which lives in the 
mollusc Cardium. Both of these larva then figured by Von Baer and 
Lacaze Duthier must be different from the present form 
McCrady, in 1873, described a bifid-tailed Cetus A 
cuculus—living in the American oyster. His figures show at once that 
the form he described is very different from the Cercaria from Jamaica. 
Other descriptions than these I do not know of, and feel reasonably 
assured that the larva has not been figured before. 
The Jamaica larva was a small, jelly-like, transparent body, being, at 
a guess, about a half a millimeter in length. It moved about quite 
actively by means of its tail. The latter structure is situated in a groove 

pd 

TREMATODE LARVA. 


