in] MOUTH-PARTS AND SENSE-ORGANS 39 



form a complicated apparatus for piercing and 

 sucking. Their construction and use cannot be de- 

 scribed without employing some technical terms. 

 When the names of the parts have been mastered, 

 a diagram will make their relative positions clear. 

 It may be necessary, first, to remind the reader who 

 is not an entomologist that the real mouth of an 

 insect is the entrance to the alimentary canal, and 

 that the appendages of the mouth, which act like 

 jaws for masticating or like tubes for sucking, are 

 really modified limbs. In fleas the mouth is suctorial. 

 But before sucking up the blood the flea must first 

 pierce the skin of its host. The paired mouth-parts, 

 then, are modified limbs which correspond with those 

 appendages on the thorax of an insect which we call 

 the three pairs of legs. 



The primitive insect, of which fleas and all other 

 insects are descendants, was, it is supposed, composed 

 of a succession of segments each bearing a pair of 

 jointed appendages. Insects of the present day never 

 have more than six legs, but the foremost pairs of 

 appendages have been bent round, reduced in size, 

 and altered in shape so as to serve as mouth-parts. 



Now the mouth-parts of the flea for which only 

 technical names exist are the maxillae and maxillary 

 palpi, the labium and labial palpi, the mandibles and 

 the labrum. The labrum is considered by some 

 authorities to be the hypopharynx. It will be best 



