76 GUIDE TO THE AUSTRALIAN MUSEUM. 



crawl on aquatic plants, and swin\ reversed on the surface of the 

 water, the Limpets cling to the rock, and the Cockles and 

 Trigonias take surprising leaps. 



The greater number of MoUusca are inhabitants of the sea, 

 some ptissing their whole life at the surface, frequently many 

 hundreds of miles from land ; others at the bottom of the ocean, 

 from which some have been dredged at a depth of four or five 

 miles from the surface ; many are foiind in shallow water, and a 

 large number between tide-marks; rivers and lakes furnish an 

 immense variety of forms ; and others live on land in all situations 

 — on mountains, in valleys, forests, and deserts. 



Molluscs are either animal or vegetable feeders, the former 

 preying principally upon other members of their own class. They 

 are classified by naturalists as in the table on pages 17 and 18. 



CEPHALOPODA.— This class includes the Octopus, Cuttle- 

 fish, tSquid, ISpirula, and the Paper and Pearly Nautilus. 



The body of the animal consists of a muscular sac, in the 

 cavity of which the viscera are placed. In front of the body pro- 

 jects the head, which in species belonging to the two-gilled section 

 of the Class, is surrounded by eight or ten fleshy arms. A Avide 

 aperture below the head admits the water to the gills or 

 branchire, which are situated in the interior of the sac, whilst a 

 short tube, the so-called funnel or siphuncle, projects from the 

 opening of the mantle — the water and various excretions being 

 expelled through this tube, especially an ink-like fluid, Avhich is 

 discharged by all Cephalopods (except Naiotilus) when disturbed 

 in order to darken the water and enable them to escaj^e from 

 their enemies. The centre of the head, between the base of the 

 arms, is occupied by the mouth, which is armed with two horny 

 or calcareous jaws, similar to the beak of a parrot. Two large 

 eyes are placed on the sides of the head. The arms or feet are 

 more or less elongate, capable of movement in any direction, and, 

 (except in Nautilus) are furnished on one side with numerous 

 suckers, by means of which the animal attaches itself most securely 

 to whatever it may seize ; they are employed capturing food and in 

 walking. Cephalopods can walk in any direction head downwards, 

 but can swim backwards only, being propelled in that direction 



