250 THE FOOD OF ANIMALS 



seen, especially if a little carmine be added to the water. A 

 similar arrangement may be noticed in the estuarine form Scro- 

 bicularia (fig. 462). 



Not infrequently the siphons are fused together, and the two 

 openings are then seen one above the other, as, for example, in 

 the Sand-Gaper (Afya arenaria), which is a common bivalve along 

 part of the British coast. 



JOINTED- LIMBED ANIMALS (Arthropoda) 



The only classes belonging to the phylum of Arthropoda that 

 require any mention in this section are those of Insecta and 

 Crustacea. 



INSECTS (Insecta) 



The great majority of Insects, so far as observations have 

 been made, feed either upon animal or vegetable matter, though, 

 as in many other groups of animals, the diet not infrequently 

 includes a small proportion of food other than the favourite kind. 

 Truly omnivorous forms are, however, known, and, as one would 

 naturally expect, these mostly belong to the orders in which 

 the mouth-parts are more or less adapted for biting. A creature 

 of this kind is the Common Cockroach {Periplaneta orientalis), 

 a member of the Straight-winged Insects (Orthoptera), the 

 structure of which has elsewhere been described (vol. i, pp. 

 343-350). At least one authority (Brunner) considers that the 

 natural food of this and other allied forms in a wild state consists 

 of dead animal matter; but be that as it may, the Cockroach is 

 undoubtedly omnivorous, though this may partly be a result of 

 its semi-domestication as an " unbidden guest ". 



Another common straight -winged Insect, the Earwig [For- 

 ficula auricularid), which is often unjustly charged with entering- 

 and damaging the human ear, also affects a mixed diet. It 

 undoubtedly devours insect larvae, small snails, &c., but also eats 

 fruit and parts of flowers, though some authorities consider this 

 is only done when the supply of animal food fails. 



Certain social Wasps and Bees are examples of omnivorous 

 Net-winged Insects (Hymenoptera). Among these are the 

 Common Wasp [Vespa vulgaris) and the Hornet {V. crabro). 

 The food consists of insects, nectar from flowers, honey stolen 

 from bees, and the flesh of various sweet fruits. The following- 



