NUTRITION AND METHODS OF FEEDING 193 



The method of feeding of higher Crustacea, as illustrated 

 by crabs, lobsters, and allied forms, scarcely needs descrip- 

 tion. It is interesting above all for the long sequence of 

 acts it involves. Before the food enters the mouth it is 

 manipulated by no fewer than seven different pairs of 

 appendages, ranging from the long, grasping chelae to the 

 stout crushing mandibles, a procedure which seems to 

 imply a higher degree of nervous control and co-ordination 

 than is required for any other method of feeding on the 

 shore. The process of mastication begun by the mandibles 

 is continued by the " gastric mill," a complicated kind of 

 gizzard, the presence of which, as we have already noticed, 

 is testimony to the tough nature of a marine diet. In the 

 general food-economy of the sea-shore the higher Crustacea 

 are chiefly important through their actively scavenging 

 habits. They are typically cryptozoic forms, lurking under 

 stones and in crevices by day, and coming out to feed when it 

 is dark. In seeking food the majority of Crustacea seem 

 to be guided more by their power of scent than of vision, 

 prawns, shrimps, and the crab Stenorhynchus, which have 

 been deprived of their eyes, having been observed to find 

 pieces of food quite as readily as when uninjured. The 

 perception of smell is in most cases obtained through the 

 antennules, though shrimps with no antennules will hunt 

 if a piece of worm is placed in their near neighbourhood 

 (Bateson, 1889). 



The habits of concealment and the occurrence of protec- 

 tive armour do not prevent crustaceans from falling frequent 

 victims to fish and cephalopod molluscs (squid, octopus). 

 The octopus is one of their worst foes and its presence in 

 large numbers has been known to have serious effects on 

 the lobster-fishery in the English Channel (Caiman, 191 1). 

 In addition to the employment of beak and suckers, the 

 octopus is said to paralyse its victims (crabs and lobsters), 

 by injecting beneath their carapace a poisonous substance 

 secreted from the salivary glands. 



The methods of feeding practised by molluscs are parti- 

 cularly varied and interesting. Perhaps the most highly 



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