cleared away, and a new muscle system must be built up suitable to the adult mechanism. Most of the other organs are transformed by a gradual replacement of cells in their tis,;ues, with the res'uit that each organ itself remains intact dt,ring the whole period of its alteration--the insect is never v«ithout a complete alimentary canal, its body wall always maintains a contint,ous st,rface. This conttition, however, is not entirely true of the muscles, fi»r with some insects t,ndergoing a high degree of meta- morphosis i,a exter,aal structure, the muscular system may st,ffer a complete disorganization, the fibers of the larval svstem being ira a state of dissolution while those of the adult are ira the process of development. The muscles ¢,f adt, lt i,sects, as we have just said, are attached to the outer
T fS1
FIG. 14o-. Diagram of the attachment of a muscle to the body walI of an adult insect by means of the terminal fibrillae (Tf M) B??/, basement membrane; Enrt, endocuticula; Epct, epicuticula; Epd, epidermis; Exct, exocuticula; Mol, muscle; Tf M, terminal fibrillae of the muscle anchored in the cuticula
and the new muscles of thc adt, I
laver of the body wall I F:ig. r42 ). This layer is composed partly of a substance called dz#in formed by the cellular laver of the body wall ??eneath it, "and constitutes the cuticuhtr skin that is shed when the insect molts. "Fhe newly- formed ct, ticula is soft and takes the con- tour of the celh, lar laver producing it. The rot, scies of the larwt that go over into the adult stage t must become fastened
to the new cuticula, and this is possible only when the cutict,la is in the soft formative stage. It has been pointed out by Powtrkoff that, for this re«tson, whenever
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INSECT
