CATERPII.LAR AND THE MOTH
it leaves the pupal skin projecting from the mouth of the cocoon (Plate I2). Concurrent with the remodeling in the external form of the insect, other changes have been taking place within the body. The first of the complicated metamorphic processes that affect the inner organs occurs in the stomach, where, as we have already observed, the inner wall is cast off at about the time that the caterpillar begins the spinning of its cocoon. This shedding of the stomach lining is quite a different thing from the molting of an external cuticula, for the StOlnach wall is a cellular tissue. Furthermore, wherever other cell lavers are discarded, as in the case of the epidermis, the cells are absorbed Mto the body cat, ity. A new stomach wall is generated usually from groups of small cells that originally lay outside the old wall and were retained when the latter was cast off. These cells, as do the imaginal discs of the epidermis, form a new lining.to the stomach and give a new shape to this organ, which in the adult insect may be quite different from that of the larva. The sheddin? of the stomach wall is hot necessarily a part of the metamorphosis, for in some insects and in certain other related animals, it is said, the stomach epithelium as well as the cuticular lining is shed and renewed with each molt of the body wall. The parts of the alimentary canal that lie before and behind the stomach, that is, the oesophagus and crop (Fig. 154, Oe, Cr) and the intestine (I??t), formed in the embrvo as ingrowths of the bodv. wall, are regenerated from groups of cells in their walls in the same manner as is the epidermis itself, the old cells being absorbed into the bodv. The cuticular linings of these parts are shed with the Cuticula of the body wall at the time of the molt. The complete alimentary canal of the moth is very different from that of the caterpillar, as will be shown in the next section of this chapter/Fig. 164). The walls of the Malpighian tubules are said to be regenerated in some insects, but the tubules do hot change
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INSECTS
