AND DEVELOPMENT OF MELOE. 169 



bony matter," and as analogous in development as in function to that of the external 

 skeleton of Chelonian reptiles. This view of its nature has recently been greatly strength- 

 ened by the discovery by Platner* of star-shaped corpuscles in the tegument of the Silk- 

 worm, very similar to those which have been described by Purkinje, Miescher, Balyf, 

 and others in true bone. 



The consolidation of the exterior tegument in insects by the deposition of earthy 

 materials in its tissue, thus appears to be a vital process precisely homologous with that 

 of the formation of bone in the Vertebrata; first by the secretion and deposition of 

 granular, earthy, crystalline matter by the nuclei and nucleoli of cells ; and next by the 

 more complete calcification of these cells in layers which form one solid envelope. This 

 process, deposition in layers, is recognized by the best observers, Hunter, Mourens, Goodsir, 

 Sharpey, Tomes and others, as the mode in which the bones of Vertebrata are increased 

 in diameter, through the agency of their periosteum, and not by the preparatory process 

 of the formation and absorption of gelatinous cartilage cells, as in their first develop- 

 ment in the foetus. According to the experience of these physiologists, the bones of 

 Vertebrata grow by the repeated deposition of layers of bony matter on their external 

 surface, formed by the progressive calcification of layers of cells from the inner surface of 

 the periosteum with which the bone is covered, as the woody fibre of exogenous trees is 

 formed, by their bark. The formation and growth of new bony matter in the skeleton of 

 Vertebrata, and the solidification of the tegument and of its internal processes in insects, 

 seem thus to be results which differ in these two divisions of animals only in degree, and 

 in the relative position of the structures in which they occur, and not in their actual 

 nature. In the Imertebrata, as in the Vertebrata, solidification is effected by deposition 

 in layers. The dermo-skeleton of the Articulata is endogenous, whilst true bone is exo- 

 genous in its mode of growth. Yet the process in both is as identical in principle as that 

 of the formation of woody fibre in the two divisions of the vegetable kingdom. The 

 solidification of the dermo-skeleton is carried to a greater or less extent in different parts 

 of the body, and at different periods of the life of the insect. In the larva, when the 

 formative energies are the most active, and the whole body is in a state of rapid growth, 

 only the exterior layers of cells become partially calcified, by the deposition of a few 

 earthy granules by the nuclei, exactly as the primary osseous deposits are known to take 

 place in the Vertebrata. But when the growth of the body begins to be arrested, prepara- 

 tory to an extensive change to the form of nymph or chrysalis, a greater number of cells 

 become calcified, and the cast-off portion of the tegument is in consequence of greater 

 thickness. Before the change to the perfect insect takes place, not only do more layers of 

 cells become altered, but fibrous tissue also appears to be developed in the most internal 

 layers, intermingled with the osteogenic ; and the two, becoming firmly solidified together, 

 thus form the insect skeleton, derived from, and inseparably connected with its dermal 

 tissues. This perhaps may explain the cause of the inseparableness of the fibrous attach- 

 ments of some of the muscles to solidified internal processes in the perfect insect, some 

 of which, as we shall find, are formed by actual reduplications of the hardened tegument. 



The whole covering of the body in the Articulata may thus be regarded as analogous in 



* Miiller's Archiv, Anat. 1844, p. 38. f Miiller's Physiology, by Baly, edit. 1, vol. i. p. 379. 1837. 



