S.A. XAT.^ VOL. XIV. 
February, 1933. By Bernard C. Cotton. 59. 
intel'lock more securely. Connecting the two large muscle scars 
is a line which follows the margin of the shell, though somewhat 
removed from it. This is formed by the numerous, small muscle- 
scars which attach the outer fleshy bag of the animal to the shell. 
At the rear end the line takes a sudden inward loop, where the 
inlet and outlet tubes project. 
Fig. 4. A . — The alimentary tract of the cockle. B . — An inside 
view of the shell. 
As an example of the Cephalopoda we might take the cuttle- 
fish (fig. 5/i). A fiat, purse-shaped creature with eight arms pro- 
vided with suckers, radiating from the head, and two tentacular 
arms capable of expansion and retraction. The eyes are well- 
developed and within the body is situated an ink bag to produce 
a protective smoke-screen effect. A wonderfully light, calcar- 
eous, honey-combed structure, the cuttlebonc (fig. 5/?)r is situated 
in the back and serves as a back-bone, though it is really the 
remains of a shell once capable of containing the whole animal, 
but now contained by the animal. It may be likened to a 
