20 ROMANCE OF THE INSECT WORLD CHAP. 



exuding a drop. The silk immediately hardens 

 on exposure to the air, and is drawn out into 

 threads equally remarkable for fineness as for 

 strength. 



In the perfect state of insects the skin may be 

 tough and thick, but still flexible ; while in the case 

 of the beetle it is so dense and hard as to appear 

 like horn. But though the variation is great, this 

 tissue is invariably composed of a peculiar substance 

 called chitine. It is formed of two layers, an inner 

 one which is soft, and not made up of chitine the 

 true skin ; the other is external and superficial the 

 epidermis,* which is capable of becoming hard and 

 horny. Both are intimately connected. It is the 

 epidermis that is cast at the transformations. From 

 its inner layers the new skin is developed, and 

 peels away as it were from the outer ones, when the 

 latter soon dry and become shrivelled and are 

 thrown off, and the new skin eventually clothes it- 

 self with a fresh epidermis. Newport infers that 

 chitine,* the basis of the insect skeleton, is inter- 

 mediate in its chemical condition between the bony 

 and dermal structures. In other words, it is bony 

 matter imperfectly developed, so modified that while 

 it affords the animal strength and solidity, it at 

 the same time admits of the performance of all the 

 organic functions of the true skin. And it may 

 be that its exuviation* is due not only to the 

 continuous growth of the insect, which causes the 

 body to become too large for the covering to contain 

 but to changes in the actual condition of the skeleton* 

 itself, dependent upon the same laws of existence 



