THE METAMORPHOSIS. 431 



are formed, which in the just excluded insect possess but half their 

 size, but fully develope themselves after this renewed change of skin. 



Among insects with a complete metamorphosis the caterpillars of the 

 butterflies moult, according to Kirby and Spence *, frequently ; but 

 thrice, according to Cuvier f. After the last moulting they become 

 pupae, and after the casting of the pupa case butterflies. The cater- 

 pillars of the Noctuae, on the contrary, moult four times, but some of 

 the large ones, which live for two years as caterpillars, much more fre- 

 quently, for instance, Euprepia villica, from five to eight times ; Eu- 

 prepia dominula, nine times ; and Euprepia caja, ten times ^. The 

 time between two nioultings also varies much, which appears to depend 

 partly upon the size of the insect and partly upon its length of life. 

 The larger ones require a longer and the smaller ones a shorter period. 

 In general the interval between two moultings varies from eight to 

 twenty days, excepting that those Lepidoptera which change into pupae 

 late in the summer or autumn, then lie the whole winter as pupae, and 

 are only fully developed upon the following spring. These pupae change 

 their larva-skin very early, mostly in the course of a few days, whereas 

 others remain long in it. This is the case in the larvae of the Tenthre- 

 donodea ; even after the pseudo-caterpillar has spun its cocoon, it still 

 remains for some weeks in its old skin, and only shortly before its time 

 of exclusion does it strip off its dried up larva case. This is at least the 

 case in the genus Cimbex, but in the smaller Tenthredos, for instance in 

 Lophyrus, in which the pupa state is of short duration, the larva skin is 

 earlier cast. Some larvae, namely, the maggots of many of the flies, 

 (Estri, Syrphodea, and Notacantha change into pupae in their larva-case. 

 All these larvae likewise possess the remarkable peculiarity that they do 

 not moult, but retain their old skin from the commencement of their 

 existence. It is in connexion with this peculiarity that we observe the 

 stronger folding of their external tunic, as also their abode in damp situ- 

 ations ; some larvae of the Syrphodea alone, namely, the larvae of Syr- 

 phus, which prey upon the Aphides, make an exception to this dwelling- 

 place, whereas on the other side many larvae moult which live in moist 

 places, namely, all the larvae of the Diptera, with many joints to their 

 antennae, for instance, those of the gnats and Tipulat, which distinguish 

 themselves from the preceding by the possession of a distinct head. The 



* Introduction, vol. iii. Nouv. Diet, d Hist. Nat. vol. vi. p. 289 ; vol. xx. p. 372. 



f Leqon's d'Anat. C'omp. vol. ii. p. 547. 



Kirby and Spence, vol. i. Lyonet, in Lesser The"ologie des Insectes, vol. i. p. 167 *). 



