434 ' LECTURE XVIII. 



culminate in the perfect insect, I should hardly have felt justified, 

 after what has been already detailed respecting the development of 

 the larva in the egg, in referring to the hypothesis of Swammerdam, 

 — that the imago was actually included in the larva, and that all new 

 skins pre-existed beneath the old one, — if such opinion had not been 

 adopted to explain the metamorphosis of insects in the admirable 

 work, already cited, of Kirby and Spence, and maintained by Cuvier 

 in the second and posthumous edition of his celebrated " Le§ons 

 d' Anatomic Comparee," where, in the eighth volume, p. 2. (1846), he 

 writes, " des I'instant ou les corps vivants existent, quelque petits 

 qu'ils soient encore, ils ont toutes leurs parties : ce n'est point par 

 I'addition de nouvelles couches qu'ils croissent, mais par le developpe- 

 ment de parties toutes pre-existantes a tout accroissement sensible." 

 The accurate observations of Herold on the changes and development 

 of the organs, during the pupa state, show these to be, like the 

 original processes of the development of the larva itself, the results 

 of a transmutation, increase, and coalescence of primitive elements of 

 the different tissues, — elements which consist of nucleated cells or 

 nuclei, like those that result from the spontaneous fissions of the 

 primary impregnated germ-cell, — elements which may be viewed as 

 parts of the original germ-mass, retained to be successively meta- 

 morphosed into the successive larval-skins, pupa-skin, and imago. 



The few instances of the reproduction of mutilated parts in insects 

 have been observed to take place only at the period of the nioult, and 

 are never manifested by the imago. A young Blatta, in which both 

 the antennas had been cut off, moulted a fortnight after the operation, 

 and then acquired two new but shorter antennae : the legs and pro- 

 legs of caterpillars are said to be produced in like manner after one 

 or two moultings. 



The passive and, as it were, embryonic condition to which most 

 insects (Coleoptera, Lepidoptera, Hymenoptera, Diptera, many Neu- 

 roptera) return when, after an active larval life, the organising 

 energies again superinduce the processes of development upon those 

 of mere growth, is called the pupa-state. The chief modifications of 

 the pupa have already been explained in relation to the terms 

 coarctate, obtected, incomplete, by which they are designated by 

 Linnaeus. 



Some pupae are protected only by the exuvial skin of the preceding 

 stage, and have been termed " naked ; " others repose in cases or 

 " cocoons," artificially prepared by the larva. The valuable silken 

 cocoons of the larva of Bomhyx mori, called, par excellence, the 

 "silkworm," are familiar examples of pupal chambers. In the 

 cocoon shown in No. 3073, of a larger lepidopterous insect ( Oiketicus 



