president’s address. 
129 
a Mollusc which cannot prevent the tube-feet of its enemy from 
maintaining a hold on its shell. Experiments were made with 
a species of Venus ( V. verrucosa), which was always attacked in 
one particular way. The Starfish places its body over its victim, 
in such a way as to form a “ mound,” beneath which the Venus is 
concealed. The Mollusc lies with its hinge below and the 
junction of the two valves in a vertical plane. The peripheral 
tube-feet are attached to the ground, on which the distal halves 
of the arms rest in a horizontal position. The proximal tube-feet 
are lixed to the two valves of the Venus, and Schiemenz believes 
that the valves are finally opened as the result of a steady pull 
exerted by the tube-feet on the two valves. The process usually 
takes from fifteen to twenty minutes, at the end of which time 
the valves are separated widely enough to allow the Starfish to 
insert its stomach between the shells; digestion taking place in 
Asterias as the result of the eversion of the stomach. 
The conclusion that bivalve Molluscs are opened by main force 
appears at first sight improbable, especially when account is taken 
of certain observations which show that a Venus can withstand 
a pulling force far greater than it would be fair to assume the 
Asterias to be capable of exerting. But Schiemenz meets this 
objection (1) by estimating by actual experiment the force which 
can be withstood by the joint action of the more centrally placed 
tube-feet of a Starfish ; (2) by showing that the valves of a Venus 
can be pulled apart by a considerably less force than this, acting 
for a prolonged period. 
The process of opening an Oyster was not actually observed, and 
it is obvious that the attitude assumed by a Starfish in relation to 
its victim cannot be precisely the same as in the case of the 
Venus, since the Oyster is attached to the ground. But reasons 
are adduced for believing that here, too, the Mollusc is opened by 
force. The shell of an Oyster has a laminated texture ; and those 
which have been attacked by a Starfish are always found to have 
parts of the outer laminae torn off until a firmer part of the shell 
has been reached by the tube-feet. It is probable that a given 
Starfish cannot overpower an Oyster of more than a certain size. 
