30 TEXT-BOOK OF ENTOMOLOGY 



moulting are white, but in a few hours turn dark, and those which 

 live in total darkness are white, showing that light has a direct effect 

 in causing the dark color of the integument. 



Moseley analyzed one pound weight of Blatta, and found plenty 

 of iron with a remarkable quantity of manganese. 



Schneider regarded chitin as a hardening of the protoplasm rather 

 than a secretion, and the cuticle is looked upon as an exudation. It 

 is structureless, not consisting of cells, and consists of fine irregular 

 laminse. "A cross-section of the chitinous layer or ' cuticle' ex- 

 amined with a high power shows extremely close and fine lines per- 

 pendicular to the laminae." In the cockroach the free surface of 

 the cuticle is divided into polygonal, raised spaces or areas which 

 correspond each to a chitinous cell of the hypodermis. (Miall and 

 Denny.) 



Numerous pore-canals pass through the cuticle of all the external 

 parts of the body. The larger canals nearly always form the way 

 for the passage of secretions from dermal cells, or connect with the 

 cavities of hairs or setae ; when very fine and not connected with 

 hairs or scales, they are either empty or filled with air, and may pos- 

 sibly serve for respiration. 



Vosseler distinguishes in the cuticle two layers of different physi- 

 cal and chemical characters. Besides the external chitinous layer 

 there is an inner layer which entirely agrees with cellulose. (Zool. 

 Centralblatt, ii, 1895, p. 117.) 



The reparative nature of chitin is seen in the fact that Verhoeff 

 finds that a wound on an adult Carabus, and presumably on other 

 insects, is speedily closed, not merely by a clot of blood, but by a 

 new growth of chitin. 



c. Mechanical origin and structure of the segments (somites, 

 arthromeres, metameres, zonites) 



The segments are merely thickenings of the skin connected by 

 folds or duplications of the integument, and not actually separate or 

 individual rings or segments. This is shown by longitudinal (sagit- 

 tal) sections through the body, and also by soaking or boiling the 

 entire insect in caustic potash, when it is seen that the integument 

 is continuous and not actually subdivided into separate somites 

 or nrthromeres, since they are seen to be connected by a thin inter- 

 scgmental membrane (Tig. !<>) But this segmentation or metame- 

 rism of the integument is, however, the external indication of the 

 segmentation of the arthropodan body most probably inherited 



