118 Journal of the Asiatic Society of Bengal. [April, 1905. 
Bronomics oF Cheetogaster bengalensis. 
The Chetogaster of the Calcutta tanks is usually found clinging 
by means of a posterior sucker to the external surface of the body 
or the edge of the shell of a water-snail. When disturbed it with- 
draws itself entirely within the latter. It does not confine itself 
to any one species of snail, but generally chooses a Limnezus, 
8 
and have a wide aperture to their shells. In one instance I saw, 
in an aquarium in which snails were somewhat scanty, a solitary 
worm attempting to establish itself on a Planorbis; but the connec- 
tion was only temporary, not lasting for more than a few minutes. 
The mouth of the shell in this genus, though there is no oper- 
culum, is evidently too constricted to be suitable for the worm, 
which is generally gregarious. As shown by the figure (plate IT, 
ing’ of a leech or a Geometrid caterpillar, but not so marked, takes 
place very occasionally. When sinking through the water, as it 
does when its hold is released, the worm can change its direction 
slightly by moving the posterior part of the body from side to side; 
_Although this species! lives in close connection with water- 
snails, it is not, strictly speaking, parasitic upon them; for it captures 
tect edi ot 
European species also live on water-snails, but some of them at any 
rate are said to be internal parasites. Dr. J. H. Ashworth has sent me 4 
specimen of an English species in which the food probably consists of 
diatoms and the like. 
