38 THE FLEA [CH. 



CHAPTER III 



THE MOUTH-PARTS AND SENSE-ORGANS 



WHEN the outward anatomy of a flea was de- 

 scribed, in an earlier chapter, the mouth-parts, which 

 form a sort of beak or proboscis under the head, 

 were mentioned. These most interesting parts of the 

 insect must now be dealt with. The reader probably 

 knows that some insects have mouths for sucking 

 fluids and others mouths for biting solids. A moth 

 or a fly cannot masticate solids, whilst a beetle or 

 a cricket has effective biting jaws. 



The first naturalist who studied the mouth-parts 

 of a flea, with such microscopes as were then avail- 

 able, was Leeuwenhoek. He was a Dutchman who 

 worked at the end of the seventeenth century, and 

 the minute accuracy of whose observations still often 

 fills modern naturalists with wonder. Microscopic 

 work was then in its early days, but Leeuwenhoek 

 clearly made out the two serrated lancets (Fig. 4) 

 which are called the mandibles. His " Microscopical 

 observations on the structure of the proboscis of 

 a flea " were published in the Transactions of the 

 Royal Society in 1706. 



The mouth-parts of fleas are differently constructed 

 from those of all other insects. Around the orifice 

 of the mouth are a number of appendages which 



