INSECTS 



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 tissues, with the result that each organ itself remains 

 intact during the whole period of its alteration — the 

 insect is never without a complete alimentary canal, its 

 body wall always maintains a continuous surface. This 

 condition, however, is not entirely true of the muscles, 

 for with some insects undergoing a high degree of meta- 

 morphosis in external structure, the muscular system may 

 suffer a complete disorganization, the fibers of the larval 

 system being in a state ot dissolution while those of the 

 adult are in the process of development. 



'Hie muscles of adult insects, as we have just said, are 



attached to the outer 

 layer of the body wall 

 ( Fig. 1 42). This layer 

 is composed partly of 

 a substance called 

 chitin formed by the 

 cellular layer ot the 

 body wall beneath it, 

 and constitutes the 

 cuticular skin that is 

 shed when the insect 

 molts. The newly- 

 formed cuticula is soft 

 and takes the con- 

 tour ot the cellular 

 layer producing it. 



The muscles of the 

 larva that go over 

 into the adult stage 

 and the new muscles ot the adult must become fastened 

 to the new cuticula, and this is possible only when the 

 cuticula is in the soft formative stage. It has been 

 pointed out by PoyarkofF that, for this reason, whenever 



[ 256 ] 



Fig. 14a. Diagram of the attachment of a 

 muscle to the body wall of an adult insect by 



means of the terminal fibrillae (Tfbl) 

 BM, basement membrane; Enct^ endocuticula; 

 Epct, epicuticula; Epd y epidermis; Exct, 

 exocuticula; Met, muscle; Tfbl y terminal 

 fibrillae of the muscle anchored in the cuticula 



