134 J. W. Fewkes—Cercaria with Caudal Sete. 
Art. XIL—A Cercaria with Caudal Sete; by J. WALTER 
FEWKES. 
THE interesting larva of a Trematode worm, described below, 
was found during my work last summer in the private labora- 
tory of Mr. Alex. Agassiz at Newport, R. I. While watching 
the water in a glass jar, for the purpose of detecting new forms 
of pelagic life, my attention was attracted by the strange 
motions of a larva swimming near the surface. At first sight 
the unknown animal was mistaken for the nauplius of one of 
our common Cirripeds, which it closely resembles in the char- 
acter of its movements. A microscopic examination, however, 
shows that it is a Cercaria, or larval Trematode, although it 
differs from any of these animals yet described. As nothing 
similar to it is to be found in the published figures of larval 
Trematodes, a figure and description is given below. e 
especially interesting feature of this Cercaria, and one which 
seems to me to justify this isolated publication of a description, 
is found in the annelid character of the tail. The larva, from 
this characteristic, may indicate some relationship which has | 
not yet been pointed out, between the worms known as the 
a 
. 
Trematoda and the Anneli 
This Cercaria is marine in habitat, and is always found at or 
near the surface of the water. The length, when the body and 
tail are extended, is about one-sixteenth of aninch. Its motion 
The head or body is in no respect characteristic. Its shape 
is very variable, being sometimes contracted into a spherical 
