16 



Class CEPHALOPODA. 



Head large, separate from the body ; eyes large, com- 

 plex, lateral ; ears developed ; mouth armed with two 

 horny or shelly jaws edged with fleshy lips, surrounded by 

 eight or ten fleshy arms, and furnished with an entire or 

 slit tube or siphuncle used in locomotion. Body ovate, 

 roundish, or cylindrical, open in front, containing the 

 viscera and one or two pairs of internal symmetrical gills ; 

 naked ; surrounded by a thin shell with a single cavity ; or 

 partly or entirely contained in the last chamber of a cham- 

 bered shell furnished with a siphon passing from chamber 

 to chamber. Individual, unisexual. Animal free, walking 

 on its head, or swimming in the sea, propelled by the 

 water from the siphon tube. 



The gills of the Cephalopods are placed within the 

 mantle, to which their stems are attached by a thin mem- 

 brane ; they are two in number, with the exception of the 

 Nautilus, where the gills are four in number, and only 

 united to the mantle by their bases. The Cephalopods are 

 all oviparous, their eggs receiving in their passage from the 

 ovary of the female a gelatinous covering, which swells in 

 the water and prevents their sinking to the bottom. 



AVhen the Cephalopods swim, they always move back- 

 wards, with the head directed downwards, and the body 

 held nearly in a perpendicular position ; they progress with 



