130 OUR HOUSEHOLD INSECTS 



the united parts constituting the mentum and sub- 

 men turn. But while in the cockroach it is obvious 

 enough that such is the origin of the labium, it is not 

 by any means so easy to make out in more highly 

 specialised insects, as the fusion of parts is in them 

 much more complete, and the whole organ is frequently 

 so greatly modified in form as to entirely obliterate any 

 resemblance to the maxillae. The cockroach is therefore 

 valuable to the philosophical zoologist, as exhibiting a 

 less altered and therefore more primitive form of this 

 organ than is to be found in the higher orders of insects, 

 and as thus shedding light upon the constitution of 

 a part of the mouth apparatus, which would otherwise 

 be more difficult to understand, The incipient ento- 

 mologist, therefore, who desires to obtain a sound and 

 practical knowledge of his science, could not do better 

 than take his first lessons in insect anatomy from this 

 very abundant and primitive species. 



After the maxillae succeed the mandibles, two broad 

 and strong jaws of simple structure, with toothed inner 

 edges, each capable of moving laterally through an angle 

 of about 30 degrees. These form very efficient biting 

 organs, and are the chief instruments for the division of 

 the food. The whole feeding apparatus, when closed, is 

 partly covered above by a central plate, the labrum. The 

 two pairs of palpi are in incessant motion, even when 

 food is not being taken, and seem to be used as tactile 

 organs, to explore the surface over which the insect 

 passes. 



The extraordinary agility of cockroaches is matter of 

 frequent comment with every housewife ; and in con- 

 sequence of their speed, and the extreme slipperiness of 

 their smooth and polished skins, they are the most 

 exasperating of insects to endeavour to catch ; while, if 



