231 



CHAPTER XV. 



INSECTA. 



(276.) The word Insect has at different times been made use of 

 in a very vague and indeterminate manner, and applied indiscrimi- 

 nately to various articulated animals. * In the restricted sense in 

 which we now use it, we include under this title only such of the 

 HOMOGANGLIATA as in their perfect or mature state are recog- 

 nisable by the following characters, by which they are distinguished 

 from all other creatures. 



The body, owing to the coalescence of several of the segments 

 which compose their external skeleton, is divided into three prin- 

 cipal portions ; the Head, the Thorax, and the Abdomen. The 

 Head contains the oral apparatus, and the instruments of the 

 senses, including the antennae or feelers, which are articulated 

 organs presenting great variety of shape, but invariably only two 

 in number. The Thorax, formed by the union of three segments 

 of the skeleton, supports six articulated legs, and sometimes four 

 or two wings ; these last, however, are frequently wanting. The 

 Abdomen is destitute of legs, and contains the viscera connected 

 with nutrition and reproduction. 



(277.) But insects, before arriving at that perfect condition in 

 which they exhibit the above-mentioned characters, undergo a series 

 of change, both in their outward form and internal structure, which 

 constitute what is generally termed their metamorphosis. When 

 this is complete, as for example in the butterfly, the insect, after 

 leaving the egg, passes through two distinct states of existence 

 before it arrives at maturity and assumes its perfect form. The 

 female butterfly lays eggs which when hatched produce, not but- 

 terflies, but caterpillars, animals with elongated worm-like bodies, 

 divided into numerous segments, and covered with a soft coriaceous 

 integument {Jig. 105, A). The head of the caterpillar is provided 

 with horny jaws and several minute eyes ; the legs are very short, 

 six of them which are attached to the anterior rings being horny and 

 pointed, while the rest of variable number appended to the posterior 



* The word Insect, derived from the Latin word Insecta, simply means divided into 

 segments. 



