196 WHEELER. [Vou. IX. 
the Planoceree were found. They creep about slowly on the 
slimy walls and between the branchial lamellz. To judge from 
the great accumulation of urates in their bodies, they probably 
feed on the nephric excretions, etc., so abundant in the bran- 
chial chamber. 
My attention was first called to the Planoceran on Sycotypus 
by my friend, Prof. H. C. Bumpus, and I gladly acknowledge 
my indebtedness to him for helping me collect a number of 
specimens of this and other Polyclads while at the Wood’s Holl 
Marine Biological Laboratory during the summer of 1892. 
I append a brief description of the parasite together with 
some notes of a morphological nature. 
Planocera inquilina, n. sp. 
The firm and compact body is quite regularly oval. In the 
adult it measures 6 mm. in length by 4 mm. in breadth. Its 
edges are not raised and gracefully curled as in so many Poly- 
clads, but remain in contact with the surface over which the 
animal is moving. Like many other planarians and pulmonate 
mollusks, P. zzguzlina is able to swim at the surface of the 
water in an inverted position. The ground color of the body 
is bluish or grayish and quite translucent, except in the center, 
where the pharynx (Fig. 1, g#) and reproductive organs (# and 
sc) are situated; these are opaque milk-white. Extending 
from this central mass very nearly to the periphery is a 
reticulum which is white in reflected and black in transmitted 
light (see right side of Fig. 1). In sections the substance 
possessing these color reactions is found embedded in the 
thick basilar membrane which immediately underlies the dorsal 
epidermis. I believe it must be some urate, although I have 
not applied the chemical test. Masses of the same substance 
are sometimes found enveloping the mature ova in the lumina 
of the uteri. It is the only substance in the body of the 
Planocera comparable to a pigment, excepting the true pigment 
in the eye-spots. In this absence of pigment P. zxguzlina 
resembles the Triclads parasitic on Limulus. These latter 
have also lost the rhabdites, but in the mollusk parasite these 
