92 ZOOLOGY. 



mantle closed beneath according to most authors, but above accordmg to 

 Eang. Most of them have three hearts. The mouth is armed with strong 

 mandibles much like those of a parrot, adapted for crushing the shells of 

 Crustacea and mollusca, and the tongue is armed with pointed horny teeth. 

 The eyes are either pedunculated or level with the surface, and they have 

 the sense of vision fully developed. They have also an organ of hearing. 

 The arms are usually cotyligerous, or studded with suckers like cif[)ping 

 glasses, which enable them to hold fish and other living prey. The Greeks, 

 in naming these sucking cups, made use of the word hotylus (in composition), 

 whence the English name cuttle-fish is derived. The cotyls are sometimes 

 armed within with curved hooks, which assist in holding and destroying 

 the prey. Onychoteuthis has a pair of arms much longer than the rest, the 

 terminal expansion of which is studded with rows of hooks, but the power 

 is increased by a simple sucker on each wrist (as it may be called), which 

 are applied together to keep the extremities of the arms in contact. 



There is a fleshy infundibulum or funnel opening before the neck, and 

 serving as an outlet for the faeces and water from the branchit-e. The water 

 ejected from the branchial sac through the funnel is a principal agent in 

 locomotion, by means of which the animal can move backwards with great 

 swiftness. Inspiration and expiration are regular in these animals. "The 

 first is efl-ected," says Dr. Coldstream, " by a gradual dilatation of the sac in 

 every direction, but particularly at the sides, accompanied by a subsidence 

 of the lateral valves, collapse of the walls of the funnel, and a rush of water 

 through the lateral openings into the sac. Inspiration being completed, the 

 lateral valves are closed, the sac is gradually contracted, the funnel erected 

 and dilated, and the water expelled through it with great force in a con- 

 tinuous stream." An OGtojJus with a sac four inches long was found to 

 respire ten times in a minute. 



The Cephalopoda are either naked, or provided with an external shell. 

 Some of the former are brilliantly colored, red, purple, or bluish, and they 

 are remarkable for the rajiidity and extent to which the colors change. In 

 habits they are rapacious and active, moving continually, and some of them 

 shoot through the water like an arrow. 



Agassiz thinks that in this order the NautilidiB are the lowest, and Sepiadie 

 the highest. We M'ill here tbllow the classification of D'Orbigny, according 

 to which the class is divided into two orders, Acetabulifera and Tentaculi- 

 fcm., the former being subdivided into two tribes, Odopoda and Decapoda^^ 

 containing seven families conjointly. As the name implies, the xlcetabulifera 

 are provided with cotyls, and the head is distinct, characters which do not 

 exist in the Tentaculifera ; and the former have two, and the latter four 

 branchit-e, whence Owen's names of Dihranchiata and Tctrahrancliiata. 



Tribe Octocera. ' 



Fam. 1. OctojndcB. The genus Octopus {0. octop>odius, Linn. {Sepia) pi. 

 76, fig. 75) is the polypus of the ancients, whence the French name poidpe 



* A name pre-occupied among the Crustacea, and on this account we employ the terms 

 Octocera and Decacera, usually attributed to Blainville. 

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