STRUCTURE OF MOUTH. 



247 



be referred to one general type of form, than the mouths of 

 the other annulose animals, some of which have a much more 

 complicated organization of the mouth than is to be found in 

 insects : thus in the crabs we find not less than five pairs of 

 jaws, whereas there are but two pairs 

 of these organs in insects. 



The parts of which the mouths of all 

 insects are composed may be reduced to 

 six; namely, four lateral pieces dis- 

 posed in pairs, and two other organs 

 opposed to each other, but in an oppo- 

 site direction, and which meet each 

 other, so as to close the mouth from 

 above and below ; the upper one being 

 placed above the upper pair of lateral 

 ^^O organs, and the lower one below the un- 

 \ m & der pair of lateral organs. 



As regards the mode of taking their 

 j^ =^ food, insects have been divided by many 

 authors into two groups ; namely, those 

 in which the mouth is furnished with 

 '- mandibles fit for biting, and those in 

 which the mouth is suctorial. All the 

 .fii T'P', la'bYai various modifications of form to which 

 we have above alluded may be referred 

 to one or the other of these sections; and it is upon 

 this character that the leading division of insects into 

 Mandibulata and Haustellata has been adopted by various 

 authors ; although, since in one period of an insect's life its 

 mouth is fitted for biting, and in another for sucking honey 

 (as in butterflies), it may perhaps be alleged that too great a 

 weight has been assigned to the structure of the mouth. The 

 jaws of biting insects have a horizontal motion ; the mandi- 



