650 CLASS IV. INSECTA. 



(b) The Holometabola have both a definite larval and pupal 

 stage. They are said to undergo complete metamorphosis. The 

 larva takes in a relatively enormous amount of nutriment, to 

 accommodate which it frequently moults. Finally it changes 

 into the almost motionless pupa. This takes no nourishment, 

 but within it the body of the insect is reconstituted into the 

 imago. This group includes the orders Siphonaptera, Neurop- 

 tera, Panorpidae, Trichoptera, Lepidoptera, Coleoptera, Strep- 

 siptera, Diptera and Hymenoptera. A certain amount of the 

 reconstruction takes place also in the late larval stages. 



The larva differs markedly from the imago both in 

 structure and habits. It is impossible within our limits 

 to describe the various forms which larvae assume. In 

 the main the form is adapted to obtaining the food which 

 they the pre-eminently food-absorbing stage of insect life- 

 eat. The characters of the various larvae are on the whole 

 secondary, and have but little value as guides to phylogeny. 

 Some larvae are to a great or less extent simplified and 

 have lost their locomotor appendages and their mouth-parts. 



Roughly speaking larvae fall into two categories. The first 

 is the so-called Campodeiform larva named after the Thysanuran 

 Campodea. and has the three primary regions or tagmata, head, 

 thorax and abdomen well defined, thoracic Avalking legs, primitive 

 biting mouth parts, and sometimes terminal appendages on the 

 abdomen. Such creatures may be found among Holometabola, e.g. 

 larvae of certain Coleoptera, but the characteristic larval stage 

 of Holometabola is the Eruciform larva, of which the best known 

 example is the Caterpillar. The skin is usually thin, the body 

 somewhat vermiform, the tagmata of the body not well defined 

 though the head is clearly marked off, the mouth parts are often 

 biting but may be much reduced, thoracic limbs usually occur, 

 and less frequently also ambulatory appendages or pro-legs. 

 The eruciform larva is typically developed in the Lepidoptera, 

 and in the Saw-flies among the Hymenoptera ; in other Hymen- 

 optera and in many Diptera it has lost many of its characters, 

 the legs and mouth-parts are reduced or absent, the head 

 very greatly reduced (some Diptera), and the larva is familiarly 

 known as a grub or maggot. The number of ecdyses is 

 often comparatively few ; whereas in the larvae of Hemi- 



