176 MR. NEWPORT ON THE NATURAL HISTORY, ANATOMY, 



its form by almost imperceptible individual differences in the development of the nuclei of 

 the multitudes of cells of which its tegument is originally composed. The greater rapidity 

 of growth in those of the dorsal region has occasioned the enlargement of that portion of 

 the body to an extent far beyond that of the region which is first formed in the production 

 of the embryo in the egg — the ventral surface — and the entire body, as a consequence, has 

 gradually assumed a totally different outline. This primary change in one region leads to 

 secondary changes in another, more especially in its appendages. We have an instance of 

 this in the gradual reduction of the legs to tubercles, their enlargement, even during the 

 feeding state of the larva, not having kept pace with that of the dorsal region ; whilst at 

 the period of change to the pseudo-larva (fig. 13), the rapid growth of this region of the body 

 not only most powerfully arrests their further development for a time, but actually con- 

 duces to a state of atrophy, as shown in their diminished size, and in the complete decidua- 

 tion of their terminal armature, the trifid prehensile claws, which we know are so important 

 to the larva in its earliest condition. This effect of rapid growth in the dorsal region is evident 

 not only in Meloe but in all larvse that undergo similar metamorphoses, Curculio, Antho- 

 phora, Ophion, and other genera. It is not the result of exhaustion of the forces of growth 

 in the undeveloped parts, but only of their retardation, the consequence of excessive deve- 

 lopment in others. In these views I refer only to the primary and essential means of de- 

 velopment in the tissues themselves, and not to those secondary ones, which are presently 

 to be examined, and by which the body of the insect is made to assume the imago form. 



The principle which operates in the deciduation of the claws, operates equally with 

 reference to the caudal styles (fig. Id), which have the same mode of origin as the per- 

 manent appendages of the segments, the limbs, of which they are the true homologues. 

 The dermal appendages, spines, hairs, and scales, are similar in their mode of origin to the 

 appendages of segments, but are not homologous with them. The latter always originate 

 by an extension outwards of an entire portion of the tegument of a segment ; while 

 hairs, spines, and scales originate in the nuclei of the cells of separate layers of tegument. 

 I have detected this origin of hairs in the embryo before it leaves the ovum. Hairs and 

 scales are developed from the more superficial layers of cells, while spines may extend 

 from the more deeply seated. Essentially their origin is the same. In like manner, when 

 either cease to be nourished, their function in the economy is at an end, they become atro- 

 phied, and are thrown off with the cast portion of tegument. This is the case alike with 

 the caudal styles and lateral hairs of Meloe, with the styles and marginal spines in Sty- 

 lops, and with the enlarged branched spines on the larvse of many Lepidoptera, changes 

 which are the result of other more important ones in the organization of the animal. 

 Function thus is the result of special structure. During the persistence of these organs 

 they are nourished as fully as other structures, and it is only when this nourishment is 

 diminished or withheld that they become atrophied. In many instances, as in the caudal 

 styles of Meloe and Stylops, and the spines in Lepidoptera, the parts involve a large por- 

 tion of the tegument, and communicate by their tubular interior with the deeper seated 

 layers, and even with the cavity of the body, as in Lepidoptera and Crustacea. In these 

 cases, the spine, originating apparently in a single cell in the embryo, gradually involves 

 other cells both around and below it in its growth, until from a single part it has become 



