102 INSECT TRANSFORMATION 



beetle larva, carries two claws. The abdomen tapers towards 

 the hinder end, its ninth segment being long and narrow ; 

 the cerci are stiff and fringed with hairs, their function being 

 to pierce the surface-film of the water in which the larva lives, 

 and thus to put a pair of tail-spiracles in touch with the upper 

 air. The lateral spiracles along the series of body-segments 

 are closed throughout larval life ; thus the Dyticus grub affords 

 an excellent example of the problem of an aquatic insect's 

 breathing being solved, not as in the case of the mayfly larva 

 and nymph by the development of special gill-structures, 

 but by provision for periodical continuity between the 

 creature's air-tube system and the atmosphere. 



The larva of a rove-beetle (the adult recognized by the 

 marked abbreviation of the elytra so that most of the abdomen 

 is uncovered) is like that of a ground-beetle in general aspect 

 and lives in very much the same way ; but it differs in having 

 only one claw on each foot. Such a one-clawed foot character- 

 izes the great majority of insect larvae, whereas in the great 

 majority of adult insects each foot has two claws. In this 

 feature, therefore, the larvae of the ground-beetle and the great 

 water-beetle show an unusual agreement with their adults, and 

 this agreement is one of the characters by which a special 

 section of the beetles (known as the Adephaga) is distinguished. 

 There are, however, other families of beetles whose larvae, 

 though they have only one claw on the foot, agree with the 

 adult insects in some other respects. 



For example, the elongate leaf-eating Silky Beetle (Dascillus 

 cervinus) has a root-feeding larva (Fig. 56, a) which may be 

 regarded as belonging to the campodeiform type though short 

 and stout in build compared with the beetle grubs already 

 described. The Dascillus larva has a very broad, prominent 

 head, and a body which tapers but slightly to the tail-end, the 

 terminal segment truncated and bearing a pair of very short, 

 stiff processes. The cuticle on all the segments is strongly 

 chitinized so that the larva has a firm, hard exoskeleton which, 

 in conjunction with its stout, spiny legs, adapts it well for 

 working its way through the soil. These legs have, as already 

 implied, only one claw on the foot ; it is in certain features of 

 the jaws 1 that the larva displays its striking correspondence 



1 G. H. Carpenter and M. C. MacDowell : " The Mouth-parts of some 

 Beetle Larvae ". Quart. Journ. Microsc. Sci., LVII. 1912. 



