METAZOA MOLLUSCA. 259 



above while in the same position. The line between the 

 two figures represents the actual length of the animals. 



After detaching itself, the young Sepia swims by means 

 of the thin border of the mantle, and only when irritated 

 uses the ambulatory pipe for darting backwards. The 

 outer skin or integument of the disc of attachment is so 

 thin that the ink bag can be clearly seen near the center 

 of it. According to Bather, 1 one larval Sepia, when 

 irritated, ejected ink twice within one minute of being 

 taken from the egg-capsule. The ink, however, was not 

 sufficiently dense to obscure the motions of the animal. 



The adult (No. 632 ; No. 633, model of the same) 

 loses the habit of attaching itself and of swimming by its 

 mantle, while the ambulatory pipe becomes the chief 

 means of rapid locomotion. The ink bag is large and 

 an efficient means of protection. The pro-ostracum or 

 pen is developed, being the calcareous portion familiarly 

 known as cuttle bone. At its base there is a vestige of 

 the chambered shell, while the guard has become nearly 

 obsolete. These animals have short, stout, bag-like 

 bodies with eight short arms and two longer ones. The 

 alcoholic specimen, No. 632, exhibits the open mouth 

 with its horny, beak-like teeth. There are two of these 

 and the lower one is the larger. The ambulatory pipe 

 is conspicuous. The cuttlefish possesses an ink bag 

 which contains the sepia used as the basis of the pig- 

 ment. 



The squid is another living representative of the more 

 specialized Cephalopods, which has lost both external 

 and internal chambered shell and has nothing but a 

 horny pen. This pen is situated in the dorsal part of 

 the mantle and can be of little use to the animal. The 

 eggs of the squid are in long, pod-like cases (No. 634), 

 which are fastened together in large clusters. In its 

 development, and in that of all Cephalopods, definite 



Journ. of Malacology, IV, No. 2, 1895. 



