INSECT A. 299 



and that the most external being removed at intervals displayed in 

 succession the skins placed underneath. Surely the advocates of 

 this extraordinary theory could scarcely have reflected upon the real 

 object of the moults in question namely, to provide a succession of 

 larger coverings proportioned to the continually increasing bulk of 

 the larva, when they advocated this strange doctrine, alike at vari- 

 ance with observation and sound physiological principles : the epi- 

 dermis and all cuticular structures are mere secretions from the sub- 

 jacent cutis or true skin ; and it can be no more necessary to suppose 

 the pre-existence of so many skins in order to explain the moults of 

 a larva, than to imagine that because, when in our own persons the 

 cuticle is removed by the application of a blister, a new layer of epi- 

 dermis is again and again produced, man should possess as many 

 skins one beneath the other. Nothing, in fact, can be more simple 

 and free from the miraculous than the whole process : at certain pe- 

 riods, when the old cuticle becomes too small for the rapidly enlarg- 

 ing dimensions of the insect, it becomes gradually loosened and se- 

 parated from the vascular and living skin or cutis by which it was 

 originally secreted, and, a new secretion of corneous matter taking 

 place, a fresh and more extensive layer of cuticle is slowly formed, 

 and then the old, dry, and dead epidermis being quite detached, is 

 split by the exertions of the larva, and the newly secreted layer placed 

 beneath it appears ; when the old skin is at length completely 

 thrown off, the newly formed one soon hardens by exposure, and the 

 re-clothed caterpillar assumes again its former activity and habits. 



(344.) Neither is the change from the larva to the pupa or chry- 

 salis less easily explained, although regarded by our forefathers as 

 being so mysterious and astonishing a phenomenon. According 

 to the hypothesis above alluded to, after removing three or four 

 skins in the embryo larva, the anatomist ought to have arrived at 

 the totally different pupa-case ready formed, and only waiting for 

 the removal of the coats above it to exhibit its characteristic form. 

 Leaving however such visionary notions, let us examine the real 

 nature of this portion of the metamorphosis. The reader will 

 bear in mind, that, whatever the form of the exterior or epidermic 

 crust, it is merely a dead and extra-vascular secretion, unchange- 

 able when once deposited. But the living skin or cutis, beneath 

 it, is, during the whole process of the metamorphosis, undergoing 

 great and important changes, increasing in size only, during the 

 larva condition ; but, when perfectly organized, developing itself 

 at different points, and expanding into variously shaped organs 



