AND DEVELOPMENT OF MELOE. 177 



a multiple of parts, which are thrown off and reproduced like the cast tegument itself, 

 until causes are induced which occasion its atrophy and decay. These causes rarely occur 

 in the Crustacea, which do not materially change their form after the earlier periods of 

 life. Hence the tegumentary appendages are usually retained in this Class as permanent 

 structures : but when secondary causes of development and change of form are in operation, 

 as in the metamorphoses of insects, then these appendages also, like the simpler dermal 

 hairs, are deciduated. The communication of the spines, in the Crustacea, by their tubular 

 cavity, with the interior surface of the tegument, as shown by a recent French observer, 

 M. Lavalle*, proves that the spine may be an eversion and extension outwards of the 

 whole tissue ; but it does not prove, as M. Lavalle seems to think, that this is its original 

 condition, but only that it may become this in the course of its growth as a spine. That 

 this is the correct explanation, and that hairs, and also scales, originate primarily in 

 the nuclei of single layers of tegument, seems proved by the fact that the skin of the 

 full-grown larva of Meloe is covered in every part with extremely minute spiniform hairs, 

 which are scarcely as much as one-thousandth of an inch in length (fig. 14). These hairs 

 proceed each from the centre of the cells which form the layer of tegument cast by the 

 insect on assuming the pseudo-larva state. These minute hairs are hollow at their base, 

 like the larger ones, and are simple eversions of the nuclei of the cells of that layer of 

 tegument ; and this also is the anatomical condition of scales. That this is the fact is 

 proved by the circumstance that not the slightest trace of these microscopic nucleus-born 

 hairs remains in the tegument of the pseudo-larva of Meloe. Still further proof is derived 

 I from the facts connected with the atrophy of the spines at the last change of tegument 

 of the larvae of Lepidoptera. In these larvae the spines, which previously communicate 

 in their interior with the deep-seated layers of tegument, have their nourishment cut 

 off, and their function in the economy destroyed, by the growth and enlargement of cells 

 in their interior, extended at their base from the deeper-seated layers of tegument ; so 

 that, on the change of the larva to a chrysalis, small tubercles only remain on the tegu- 

 ment in places previously occupied by elongated and powerful spines. 



It is in this way that not only hairs and spines, but also the armature of the distal ex- 

 tremities of the limbs, the claws, are thrown off, and the limbs themselves become atro- 

 phied, by deciduation of their external covering, from without inwards, as well as by 

 actual retardation of growth : both of these results are induced to a greater or less extent 

 in proportion as other parts or regions are enlarged. 



These are some of the primary laws of the organization and growth of structure, the 

 formation of which, thus commenced, is further advanced by secondary ones ; and develop- 

 ment is hastened or retarded by the operation of physical conditions, — light, heat, food, 

 and all material influences. 



To pass now from the primary stages of growth and change to the secondary, by which 

 further development is effected, we must first examine the structure of the layer of tegu- 

 ment which the full-grown larva throws off on assuming that state in which alone I have 

 hitherto found this insect — the pseudo-larva. This cast portion always partially envelopes 



* Annales des Sciences Naturelles, 3 me Sene, 1847. 



