192 THE . ZOOLOGIST. 
or grappling-iron, and when in the act of gripping the tufts expanded like 
ahand. It was evident therefore that these worms were specially adapted ™ 
for clinging firmly to their host, and I found it rather difficult to detach 
them ; but with the assistance of a friend, who is rather clever in manipu- 
lating for the microscope, I managed to get one mounted. The head of the 
worm, I noticed, was ciliated, and there were from four to six worms on this 
specimen, if [ remember correctly. I omitted to make a note of it, although 
on others I found fully six worms. 
The conclusion one would naturally draw from the above facts is, I 
think, that the irritation produced by several of such worms, or possibly the 
desire of the mollusc to accommodate them, is sufficient to account for the 
depression of the head and the consequent distortion of the shell. On exam- 
ining two normally formed specimens of Planorbis complanatus, I found 
that one carried worms and that the other did not. It does not, however, 
follow that because one animal carried worms and had a normal shell, that 
therefore my theory will not hold good, since the worms might have only 
recently attached themselves, and the amount of irritation would naturally 
be proportionate to the number of worms. I may here mention that the 
Planorbis was only half-grown, and that the head and tentacles were strongly 
ciliated. It may be that the worms derived some advantage from this 
circumstance, since in very stagnant water the currents set up would bring 
both food and oxygen. But I imagine that the main benefit derived would 
be from the fact of being transported about, and that from a position of 
sreat security, Under irritation the worms evinced an uncontrollable desire — 
to divide. This operation was performed once, and almost a second time. 
A constriction took place at a certain point in the body, and gradually 
became more and more pronounced. ‘Then the body from time to time 
gave some spasmodic twitches and bent upon itself at the constricted point. 
A few more spasmodic twitches followed, and the trick was done. 
From the facts here stated J think a fairly good prima facie case is made 
out, and if other observers who happen to meet with scalariform Helices, 
&c., would examine the head closely, they would most likely find some 
irritating parasite to account for the abnormality. 
On mentioning the above circumstances to a gentleman at South Ken- 
sington Museum, he cited the case of a scalariform Turritella, which when 
found had on its head a parasitic crustacean. The name of the worm above 
alluded to is Chatogaster limnai, Von Baer. — P. Rurrorp (The Croft, 
Hastings). 
