18 
W. J. Dakin 
function of certain sense organs. No results have been published of 
any experiments made to determine the function of the osphradia, oto- 
cysts, and abdominal sense organs of the lamellibranchiata. Freiden- 
dELT (1897) stated that he was making some experiments on the osphra- 
Fia, but nothing has been published so far as I am aware. As regards 
the otocysts, experiments have been made on cephalopods by Fröhlich 
and I believe by Dr. Bauer on Pecten . I found that Pecten was, as most 
lamellibranchs would be, a difficult example for the purposes of such 
research and the results have not been as satisfactory as I had hoped. 
They are given here, since they are connected naturally with the 
description of the anatomy of the ganglion and it may be some 
time before I shall be in a position to continue the same experiments. 
Pecten lives on the sea bottom (mud, sand or shelly) and certain 
speci es are at times attached by byssus in the adult stage whilst others 
like Pecten maximus are entirely free. If a number of specimens of 
Pecten opercularis or P. jacohaeus are kept in a large aquarium tank, 
they will be seen occasionally to rise from the bottom and swim a short 
distance by rapidly opening and closing the shell, until after progressing 
in this way they come perhaps into contact with the sides of the tank 
or simply cease their movement and fall slowly to the bottom. This 
action appears to be quite spasmodic and without any causing Stimulus, 
except that a commotion made in the water may sometimes start one 
individuai off and then the movement is apparently communicated to 
others. This latter action is however as a rule only seen when the ani- 
mais are quite fresh from the sea and not after a sojourn in the aquaria. 
Usually no ordinary Stimulus will start a Pecten swimming, and disturb- 
ing the animai, irritating the mantle edge, casting a shadow on the eyes, 
or turning the animai over is simply foUowed by a more or less rapid 
closure of the valves and perhaps a dart back from the irritating object. 
It was found however how this response could be produced, through 
noticing the effect of throwing some starfish into the Pecten tank, and 
discovered that the animals could be set off swimming by bringing a 
specimen of Ästerias rubens in close proximity to the various indivi- 
duai. I have since heard that others have observed this phenomenon, 
but the experiments were not carried any further nor has any note on 
the subject been published. It was impossible to say whether touch, 
sight or smeli was the factor concerned without further experiment. 
For some time a large number of Pecten opercularis, were kept in a 
tank and these were repeatedly disturbed by knocking, and touching 
the valves in various ways without however producing any effect com- 
