TR AC HE AT A. 349 



In the Diptera the larvae are apodous. In the true flies (Muscidoe) tliey 

 are without a distinct head and have the jaws replaced by hooks. In the 

 Tipulidse there is on the other hand a well developed head with the normal 

 appendages. The pupae of the Muscidae are quiescent, and are enclosed in 

 the skin of the larva which shrinks and forms a firm oval case. In the 

 Tipulidse the larval skin is thrown off at the pupa stage, and in some cases 

 the pupae continue to move about. 



The larvae of the Neuroptera are hexapodous voracious forms. When 

 the larva becomes a pupa all the external organs of the imago are already 

 established. The pupa is often invested in a cocoon. It is xisually 

 quiescent, though sometimes it begins to move about shortly before the 



imago emerges. 



In the Coleoptera there is considerable variety in the larval forms. As a 

 rule the larva? are hexapodous and resemble wingless Insects. But some 

 herbivorous larvae (e.g. the larva of Melolontha) closely resemble true 

 caterpillars, and there are also grub-like larvae without feet (Curculio) 

 which resemble the larvae of Hymenoptera. The pupa is quiescent, but 

 has all the parts of the future beetle plainly visible. The most interesting 

 larvae among the Coleoptera are those of Sitaris, one of the Meloidse (Fabre, 

 No. 409). They leave the egg as active hexapodous larvae which attach 

 themselves to the bodies of Hymenoptera, and are thence transported to a 

 cell filled with honey. Here they eat the ovum of the Hymenopterous 

 form. They then undergo an ecdysis, in which they functionally lose their 

 appendages, retaining however small rudiments of them, and become grubs. 

 They feed on the honey and after a further ecdysis become pupa?. 



In tli3 Lepidoptera the larva has the well known form of a caterpillar. 

 The caterpillars have strong jaws, adapted for biting vegetable tissues, 

 which are quite unlike the oral appendages of the adult. They have three 

 pairs of jointed thoracic legs, and a variable number (usually five) of pairs 

 of rudimentary abdominal legs the so-called pro- legs. The larva undergoes 

 numerous ecdyses, and the external parts of the adult such as the wings, 

 etc., are formed underneath the chitinous exoskeleton before the pupa 

 stage. The pupa is in some moths enveloped in a cocoon and is known as 

 a chrysalis. 



The Hymenoptera present considerable variations in the character of 

 the larvae. In the Aculeata, many Eiitomophaga, the Cynipidae, etc., the 

 larvae are apodous grubs, incapable of going in search of their food ; but in 

 the Siricidae they are hexapodous forms like caterpillars, which are some- 

 times even provided with pro-legs. In some of the Eiitomophaga the larvae 

 have very remarkable characters which have already been described in a 

 special section, vide p. 346, 347. 



Before proceeding to the consideration of the value of the various 

 larval forms thus shortly enumerated, it is necessary to say a few 

 words as to the internal changes which take place during the oc- 

 currence of the above metamorphosis. In the simplest cases, such as 

 those of the Orthoptera and Hemiptera, where the metamorphosis is 

 confined to the gradual formation of the wings, etc. in a series of 

 moults, the wings first appear as two folds of the epidermis beneath 

 the cuticle on the two posterior thoracic segments. At the next moult 

 these processes become covered by the freshly formed cuticle, and 



