THE CEPHALOPODS. 271. 



the senses are as highly developed as in the fishes, in others thej 

 are confined to the narrow perceptions of the polyp. Many 

 are individually so small as to escape the naked eye, others of 

 a size so formidable as to entitle them to rank among the giants 

 of the sea ; some are perfectly harmless and unarmed, others 

 fully equipped for active warfare. It is evident that creatures 

 so variously gifted, and consequently so widely dissimilar in 

 structure, cannot possibly be grouped together in one description, 

 and that each of the four orders, Cephalopoda, Gasteropoda, 

 Pteropoda, and Acephala (Lamellibranchiates, Brachiopods, 

 Polyzoa, and Tunicata), into which they have been subdivided, 

 must be separately brought before the reader, in order to give 

 him a clear and faithful picture of their organisation and mode 

 of life. 



The Cephalopods are the most perfect specimens of the 

 molluscan type, as the decapods are the first among the 

 crustaceans. These remarkable creatures consist of two dis 

 tinct parts : the trunk or body, which, in form of a sack, 

 open to the front, encloses the branchias and digestive organs, 

 and the well-developed head, provided with a pair of sharp- 

 sighted eyes, and crowned with a number of fleshy processes, 

 arms or feet, which encircle and more or less conceal the mouth. 

 It is to this formation that the cephalopod owes its scientific 

 name, for as the feet grow from the circumference of the mouth, 

 it literally creeps upon its head. 



All the cephalopods are marine animals, and breathe through 

 branchiae or gills. These are concealed under the mantle, in 

 a cave or hollow, which alternately expands and contracts, and 

 communicates by two openings with the outer world. The one 

 in form of a slit serves to receive the water ; the other, which is 

 tubular, is used for its expulsion. 



According -to the different number of their gills, the 

 cephalopods are divided into two groups. The first, to which 

 the poulp and common cuttle-fish belong, and which comprises 

 by far the majority of living species, has only two sets of gills ; 

 while the second, which, in the present epoch, is only 

 represented by a few species of Nautilus, has four, two 

 on each side, according to the number of their arms or feet — 

 for these remarkable organs serve equally well for prehension 

 or locomotion. The first group is again subdivided into two 



