34 THE FLEA [CH. 



The older authors, Linnaeus, Geoffroy, Cuvier and 

 Dunieril, and Gervais placed them among the Aptera 

 because they were wingless. Kircher regarded 

 them as Orthoptera, an order which includes grass- 

 hoppers and crickets ; but he has had few followers. 

 By Fabricius and by Illiger they were treated as 

 Hemiptera or bugs. Lameere, a Belgian, has 

 recently expressed a decided view that fleas are 

 really a family of Coleoptera or beetles. Those who 

 have held the once orthodox opinion that they 

 belonged to the Dipt era or flies are Roesel, Oken, 

 Straus-Durkheim, Burmeister, Newman, Walker, von 

 Siebold and Wagner. 



The structure of an adult flea, however, differs 

 from that of an adult fly in the following note- 

 worthy respects : the mouth-parts are differently 

 constructed, the head of the flea is closely joined 

 to its thorax, the three divisions of the thorax 

 are not joined and fused, the flea is wingless, the 

 eyes of fleas are simple ocelli, and there are differ- 

 ences of lesser importance in the stigmata, which 

 give access to the tracheal system by which all 

 insects breathe. 



The number of those who have regarded fleas as 

 belonging to a distinct order of insects is consider- 

 able : they are Lamarck, De Geer, Latreille, Kirby 

 and Spence, MacLeay, Leach, Duges, Bouche, van 

 der Hoeven, Westwood, Landois, Brauer, Kraepelin, 



