22 
W. J. Dakin 
what deeply situated and, owing to the sinus like character of the blood 
system, it is impossible to perform the Operation without a considerable 
loss of blood. The result is always a great shock to the nervous system. 
It was surprising to find that some of the specimens operated upon lived 
for some time afterwards, and might have recovered if placed under 
normal conditions in the sea. Most of the animals however, died. It 
is difficult to place any reliance on movements taking place immediately 
after the shock, and it is hardly likely that a turning movement will be 
obtained later, since the uninjured animai after a sojourn in the aqua- 
rium often falls to react. In no case did any of my specimens turn over, 
after the connectives had been cut, and usually the shell remained closed 
for some time. On one or two occasions however, there were a few spas- 
modic movements when the animai was released and placed in the water, 
which resembled those made if the mantle edge be suddenly irritated. 
It might be that one of Dr. Bauer's specimens overturned itself in this 
way. 
I believe that the otocysts are concerned with orientation and though 
we have no direct proof, yet the severing of the cerebro-visceral con- 
nectives was not foUowed by overturning when the animals were placed 
on the left side. The results of experiments made in like organs of the 
cephalopoda, lends strong support to this view. After the cerebro-vis- 
ceral connectives had been cut, and the shell valves were once more opened 
after recovery from the shock, it was seen that the animals were just as 
sensitive to touch, and to waves caused by tapping the sides of the tank 
in which they were contained. These caused an immediate closure of 
the shell, and it was evident that the Vibration was perceived by sensory 
endings in connection with the visceral ganghon. The Separation of the 
otocysts from the visceral ganghon, did not interfere with the perception 
of these waves in the water. 
Remo vai of the abdominal sense organ did not interfere in the least 
with the orientation of the animai when it was placed upon the left side, 
and in fact, it was impossible to discover any effect caused by removal 
of this sense organ. Stimulation of the organ in uninjured animals pro- 
duced no effect whatever. The function of the abdominal sense organ 
remains very obscure. Thiele, the discoverer, believes that it is like the 
sense organs of certain chaetopoda, for the purpose of perceiving move- 
vements in the water. As shown above the removal of this organ does 
not affect the sensitivity of the animai to such movements, in the slightest 
degree. Pelseneer beheves that the abdominal sense organ has the 
function like the osphradia of testing the quality of the respiratory fluid. 
