136 PHYSIOLOGY OF INSECTS. 



the Entomologists of this country, it was abandoned. The 

 terms now used are in accordance with those employed in 

 the essay in question. 



The chapter terminating the history of insects, and treat- 

 ing of their transformations, may perhaps be more strictly 

 applicable to the present branch of the subject ; but the 

 author trusts that those graver and more scientific pages will 

 serve, in some measure, to exjtlain the changes previously 

 described, and lead the enquiring mind to seek further 

 information on the highly interesting subject of insect 

 l^hysiology. In the chapter in question it has been ex- 

 plained that insects, instead of an internal framework of 

 bones supporting the softer parts, have their external skin 

 or covering indurated, incrassated, ossified, invested with 

 powers possessed by a skeleton or framework of bones, 

 and fulfilling the very offices for which such a framework 

 is designed, namely, supporting the softer parts, and afford- 

 ing points of attachment for the muscles. This indurated 

 skin envelopes the animal in the manner of a suit of ar- 

 mour, enclosing and protecting from injury those parts 

 which are softer and more immediately connected with 

 vitality: in its composition this skeleton possesses more or 

 less of the elements found in the bones of vertebrated 

 animals. 



In order to admit of perfect freedom in the performance 

 of those numerous acts in which an insect's life is passed, 

 it is essential that this bony covering should be possessed 

 of the power of turning to the right or left, upwards or 

 downwards ; otherwise constant difficulty must occur. To 

 accomplish this, the body, which is very long in proportion 

 to its breadth, is divided into thirteen segments, the inter- 

 stices between these being filled up by a softer and more 

 flexible portion of the same skin. This division of the 

 body into segments is exhibited very clearly in the earlier 



