n] EXTERNAL STRUCTURE OF A FLEA 37 



jaws, are somewhat reduced and rudimentary. The 

 absence of eyes and of legs are points of similarity 

 between the larvaa of fleas and flies. The maggot 

 of a fly has also two pairs of jaws, and a pair of 

 antennae. 



At the tail end of the larval flea's abdomen are 

 two small projections called caudal stylets (Fig. 1). 

 They are strong, recurved, chitinous, structures which 

 prop up the body of the larva when it creeps and 

 wriggles. There are similar props in the larvae of 

 certain beetles and no exactly similar organs are 

 known in dipterous larvae. But caudal stylets are 

 of small taxonomic importance. 



In one respect the mature flea is certainly nearer 

 to a beetle than to a fly : the three joints of the thorax 

 are free as in a beetle and not fused as in a fly ; 

 but when one studies the mouth-parts, the true view 

 seems to be that the mouth-parts of a flea are 

 equally unlike those of a fly and those of a beetle. 

 Such being the present state of our knowledge, one 

 must wait for fresh light to be thrown on the matter 

 by further researches. It seems unlikely that the 

 immediate future will produce a solution of the 

 problem. 



