432 PHYSIOLOGY. 



reason, therefore, why these larvae do not moult cannot lie exclusively 

 in their damp place of abode ; nor that their existence as maggots is 

 but of short duration, as, for example, in the common flesh fly from 

 eight to ten days, but it must be found in other conditions of their organ- 

 isation which have not yet been discovered. Besides, this phenomenon 

 also proves that the development of insects of different orders, and even 

 of the different families of the same order, can take place in a different 

 manner, and that, therefore, the assertion that the intestine also moults 

 in some orders, whereas in others it does not, is not so wholly gratuitous; 

 but we will nevertheless not decide, having made no observations upon 

 the subject. The determination in another instance is just as difficult, 

 and in which also the observations of several naturalists stand in direct 

 contradiction : this is the case in the maggot of the bee. This, accord- 

 ing to Reaumur and Huber's observations *, like all the apode larvae 

 of the Hymenoptera, consequently in by far the majority, does not 

 moult, but merely gradually grow larger. Whereas Swammerdamm 

 says expressly that he has observed the moulting of the larva of the 

 bee f, and that he has likewise found the inner tunic of the intestinal 

 canal in the caecum behind the stomach of the maggot of the hornet J. 

 However the case may be, we prefer adopting the first opinion, as all 

 these larvae exhibit a very great conformity with those of the Diptera, 

 which certainly do not moult. This conformity refers not merely to 

 the larva, but likewise considerably to its mode of life, in as far namely 

 as that the larva of the (Estri, as well as the maggots of the pupa- 

 phaga, are true internal feeders. But they in so far differ from each 

 other that the hymenopterous larva casts its skin when it becomes a 

 pupa ; the larvae of these Diptera, however, change into pupa within 

 their larva skin. In Slratiomyx, indeed, the shape of the larva remains 

 unaltered, and it was thence that Knoch considered this larva an 

 annulate worm, in which the larva of the Stratiomys lived as a para- 

 site || : in the rest, however, the soft skin of the larva shrinks up into 

 an egg-shaped, hard, annulated case, in which the pupa is concealed, 

 with its free and visible limbs. The other Diptera, which moult as 

 larvae, cast their larva skin before changing into the pupa state ; this 

 is the case, for instance, in the larvae of the gnats, of the Asilica, Xylo- 

 phagi, and many others. 



* Kirby and Spence, vol. iii. t Biblia Naturae, p. 163, a. Ib. p. 133, a. 



|| Neue Beitriige zur Insektengescliichte, PI. I. 



