INTERNAL METAMORPHOSIS. 323 



therefore called campodeiform. It has the regions of the 

 body well defined, three pairs of locomotor thoracic limbs, 

 and mouth parts adapted for suction, (fr) The other type is 

 worm-like or cruciform, e.g.) the caterpillars of- butterflies and 

 moths, with three pairs of limbs ; the more modified grubs of 

 bees, &c., with distinct head, but without limbs ; and the 

 degenerate maggots of flies, &c., not only limbless, but with 

 an ill-defined head. But the caterpillar has often several 

 pairs of abdominal pro-legs, which may be homologous with 

 legs, and other abdominal appendages are known on the 

 larvae of other insects, and even in the embryos of some 

 whose larvae are campodeiform. These facts make it likely 

 that the primitive form had many legs. 



The larvae of Insects vary enormously in habit and in structure, and 

 exhibit numerous adaptations to conditions of life very different from 

 those of the parent. Thus caterpillars, which are usually plump and 

 tense, so that a peck from a bird's bill may cause them to bleed to death, 

 even if no immediate destruction befall them, are protectively adapted 

 in many different ways. Their colours are often changed in harmony 

 with those of their surroundings, some palatable forms are saved by 

 their superficial resemblance to those which are nauseous, a few strike 

 " terrifying attitudes," others are like pieces of plants. 



But for our purpose it is perhaps more important to recall the 

 differences between the respiration of some larvae and that of the adult, 

 between the apneustic larva of the dragon fly and the holopneustic 

 winged tyrant. Likewise of great importance, and supplying a basis for 

 classification, are the changes in connection with the mouth organs. The 

 main facts may be summarised in a terse sentence from the monumental 

 work of Rolleston and Hatchett Jackson " Forms of Animal Life," 

 Oxford, 1888). " The mouth parts may be similar in all stages of life, 

 and then are either adapted for biting (Menognatha^ i.e., jaws persistent), 

 or for sucking (Menorkyncha, i.e., proboscis persistent), or else they are 

 adapted in the larva for biting, in the adult for sucking, the change 

 commencing in the pupa, and rarely affecting the larval ^^(Metagnatha, 

 i.e., jaws changed)." 



Internal Metamorphosis. 



In Insects with no marked metamorphosis, or with an 

 incomplete one merely, the organs of the larva develop 

 gradually into those of the adult. But in Insects with 

 complete metamorphosis, there is a marvellous internal 

 reconstruction during the later larval, and especially during 

 the quiescent pupal stage. Most of the larval organs are 

 disrupted and partially absorbed by amoeboid cells, their 

 debris being used in building new structures. Parts of larval 



