248 SELIG HECHT 
It will be noticed that the general shape of the curves produced 
by the closing and opening of the siphon rims resembles that of 
the contraction and recovery of smooth muscle (Winkler, ’98). 
The effective agent in the closure is, indeed, the sphincter of 
smooth-muscle cells in the siphon working against the elasticity 
of the tissues and the test. Although the presence of the test 
undoubtedly helps in the opening of the rim, the recovery from 
the contracted condition can occur without the test. Animals 
a 
yo 
oe 
CANO 
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i a AU 
iy, 
Fig. 9 Right side of animal with the test removed. h., heart; l.m., longitudinal 
muscles; t.m., transverse muscles. 
from which the test had been removed were still capable of 
closing and opening the siphons. It seems reasonable to suppose 
that the elasticity of the tissues which is responsible for this 
recovery is due to the presence of spaces filled with blood under 
pressure. 
2. Body movemenis 
The bending of the body on its long axis occurs so that the 
right side of the animal always forms the concave surface of the 
bend. This is accomplished by the contraction of longitudinal 
muscle strands which lie on the body wall of the right side only 
