282 



CLASSIFICATION OF ANIMALS 



mantle is very thick and muscular. The foot is shaped like a funnel and 

 projects somewhat beyond the edge of the mantle. By the strong con- 

 traction of the mantle a stream of water is shot out through the funnel 

 which causes a backward movement of the animal. Less vigorous con- 

 tractions of the mantle produce respiratory currents. The large head is 

 produced into eight or ten long arms which encircle the mouth. The oral 

 surface of the arms is covered with numerous suckers which are purely 

 hold-fast organs. The mouth opens into a buccal cavity and is provided 

 with two strong jaws which together have the form of a beak. The buccal 

 cavity contains a radula, and into it open four large salivary glands. The 



Fig. 167. — The Devil-fish (Octopus), a dibranch Cephalopod. A, At rest; B, 

 swimming, a, Arms; e, eye; s, siphon. (From Galloway after Merculiano.) 



long oesophagus is sometimes enlarged into a crop. The stomach consists 

 of two sacks into one of which two large digestive glands open. A large 

 gland secreting ink opens into the rectum near the vent. The vent opens 

 into the mantle cavity. The ink is discharged when the animal is pursued 

 and serves to cover its flight. The heart lies in the upper side of the 

 visceral mass. It consists of a ventricle and as many auricles as there are 

 gills, 2 or 4. The arteries entering the gills are enlarged, muscular and 

 rhythmically contractile. They are called branchial hearts. There are 

 one or tw^o pairs of kidneys intimately connected with the circulatory 

 system and also connected with the body cavity by nephridial funnels. 

 The kidneys open into the mantle cavity. 



