20 THE FLEA [OH. 



into a groove at the side of the head and can be 

 protruded when desired. This is another adaptation 

 to enable the insect to creep swiftly through a forest 

 of hairs. 



The combs which are found on the heads of many 

 fleas are organs of exceptional interest (Fig. 2). 

 They are toothed and horny appendages, which are 

 connected with parasitic habits, for somewhat similar 



a 



Fig. 2. Showing a type of (a) genal and (b) thoracic combs 

 of a flea, on the under part of the head and on the 

 thorax respectively. Analagous combs are found in 

 several other parasitic insects and on the abdominal 

 segments of certain fleas. 



combs are found on several unrelated groups of 

 parasitic insects, as, for instance, on parasitic beetles 

 (Platypsyllus] found on the beaver, on insects allied 

 to bed-bugs (Polyctenes) found on bats, and on wing- 

 less flies (Nycteribia) which infest Egyptian and 

 South American bats. The majority of the Puli- 

 cidce have one or more combs with comparatively 

 long teeth. These combs reach their maximum 



