DIBRANCHIAL CEPHALOPODS. 27 



16. The family of Cephalopoda, Dibranchiata, — or Ace- 

 tabuli'fera, — that is, cupping-glass bearers, is very numerous. 

 In it are placed the poulpes, cuttle-fishes, calmaries, argonauts, 

 &;c. Most of these moUusks have no external shell, and their 

 naked skin includes a great number of contractile vesicles, filled 

 with differently coloured fluids, which, by alternately contracting 

 and expanding, produce and cause again to disappear, in turn, 

 often very brilliant spots; but we find in their interior a more or 

 less developed shell, situated on the back. This shell is largest 

 in the cuttle-fishes ; it is oval, and composed for the most part of 

 a great number of transverse calcareous laminse ; it is very com- 

 mon on the sea-shore, and is generally known under the name 

 o'i cuttle. -fish hone. In the calmaries it is of a horny consistence, 

 and in its form resembles a feather or lamella ; and in the poul- 

 pes it is merely represented by two horny stylets, lodged in the 

 thickness of the mantle. 



17. The tentacula of these cephalopods form a simple crown 

 around the mouth, and bear on their internal face circular cups 

 or suckers, the number of which varies from eight to ten. In 

 the following family we shall find an entirely different arrange- 

 ment. 



18. The Poulpes — Octopvs {Fig. 7, Page 19) — are easily 

 recognised by their naked body, which is in the form of an 

 oval sack, unprovided with fins, and their eight very large and 

 nearly equal feet. They make use of these last organs to 

 seize their prey as well as to swim and crawl upon the ground, 

 and are even formidable to swimmers on account of the force 

 with which they press those bodies they embrace. These ani- 

 mals are essentially carnivorous. Their size is often very great : 

 there is one species in the Pacific Ocean which attains about 

 six feet in length. These mollusks are objects of terror to 

 the natives of the Polynesian Islands, who dive to the bottom 

 of the sea for shells; but their size and strength are wonder- 

 fi.illy exaggerated. Pliny speaks of a poulpe that had arms 

 thirty feet long; and a modern author gravely relates the 

 history of one of these gigantic mollusks, which, attacking a 

 vessel, nearly upset it ! The Common Poulpe — Sepia Octopo- 

 dia — is about two feet long; it inhabits the coasts of Europe, 

 and commonly keeps among rocks : it destroys a great many 

 fishes and Crustacea. 



16. What are the general characters of the cephalopoda dibranchiata? 

 What is cuttle-fish bone? 



17. How are the tentacula of cephalopods arranged? 



18. What are the general characters of the poulpes ? What is the nature 

 of their food ? Where are they found ? 



