STRUCTURE OF CEPHALOPODS AND PTEROPODS. 117 



the fin-like tail, by which the animal is propelled through the 

 water very much in the manner of a fish. The Pearly 

 Nautilus is the only type now existing of an inferior order of 



Fig. 57. CALAMARY. 



Cephalopods, which approaches the Gasteropods in many parts 

 of its organization. The body is inclosed in the last chamber 

 of a shell (usually spiral in form), 

 the cavity of which is divided by 

 numerous transverse partitions ; and 

 such shells, the fossilized remains of 

 very numerous forms of this group 

 that existed in the ancient seas, con- 

 stitute the nautilites, ammonites, 

 belemnites, &c., which abound in 

 many rocks (fig. 58). The Cuttle- 

 fish are animals of considerable 

 activity; their mouth is furnished Fig SS 

 with a horny beak, strongly resem- 

 bling that of the parrot ; and their arms are provided with 

 a series of very curiously constructed suckers, by the action 

 of which they can take a very firm 

 hold of anything which they desire 

 to grasp. 



112. The class of PTEROPODA, or 

 wing-footed Mollusks, consists of 

 but few species, and the animals 

 which it contains are all of them of 

 small size ; but the individuals are 

 often very numerous, whole fleets 

 of them being sometimes seen 

 covering the ocean, especially in 

 the Arctic and Antarctic regions, 

 where they constitute one of the Fig> 59 -- HTAI -* A - 

 principal articles of food to the Whale. The general form of the 

 body usually differs but little from that represented in fig. 59. 



