OBSERVATIONS ON COLEOPTERA. 



185 



tion periods the cells are hexagonal 

 flattened epithelial and of them- 

 selves would be a relatively weak 

 layer if left alone. In the period 

 of preparation, however, the inner J 

 ends elongate, the basement mem- | 

 brane draws away and the cells i- 

 come to form a much thicker layer, -| 

 until during the period of ecdysis 

 they present the condition shown 

 in Fig. 7, D, which arrangement, 

 even though the thick cuticle be 

 absent, gives a far greater rigidity 

 to the body wall than the arrange- 

 ment seen in Fig. 7, A, After | 

 ecdysis is over the cells gradually = 



W ' 



assume their epithelial character. -3 

 This series of change represented | 



<u 



in Fig. 7 evidently is for no other 

 purpose than that of making the 

 integument as rigid and strong as 

 possible during ecdysis. The ar- 

 rangement developed is one which 

 in a mechanical way is the best 

 possible under the conditions. In 

 fact the arrangement of the base- 

 ment membrane, the long drawn 

 out hypodermal cells and the devel- ^ 

 oping cuticle is exactly the system -g 

 used by engineers in large bridge 

 work or in the building of large 

 spans or girders. 



The change in the integument 

 are all in the direction of strength- 



c.' 



h. 



B. 



D. 





F. 



G. 



FIG. 7. Diagrammatic representation of stages passed through by the hypodermis 

 before, during and after ecdysis, to show changes in the form of cells. c f , primary 

 cuticula ; c 2 , second cuticula; <- 3 , old larval cuticula being removed; //, hypodermis ; 

 tub, basement membrane. All figures are horn preparations of L. decimlineata. 



