n] EXTERNAL STRUCTURE OF A FLEA 27 



development in the bat-fleas which have no less 

 than eight. Some Australian and South American 

 fleas (Steptianocircus) have a helmet-like comb 

 extending all round their heads. These combs are 

 by some supposed to be of service in holding on to 

 the hairs of the host ; and, if one may judge from 

 experiments made on live fleas in cotton wool, they 

 are also used in moving forwards through the fur. 



All the chigoes (Sarcopsyllidce] have a large 

 triangular post-oral process which is more or less 

 curved and probably prevents the flea slipping back 

 as it pushes forward. Bat-fleas (Ceratopsyllidai) 

 have lobes or flaps placed two on each side of the 

 head, which may possibly serve an identical purpose, 

 but whether they do so is not known. 



These combs may be divided into three groups 

 according to the part of the flea's body on which 

 thev are found. Those found on the head are called 



/ 



genal combs and take the form shown in Fig. 2. 

 There are also combs found on the thorax. The 

 fossil flea (Palceopsylla Idebsi) described in the 

 previous chapter has one of these thoracic combs. 

 A certain number of fleas also have combs on the 

 abdominal segments. 



There are really two types of toothed organs on 

 fleas to both of which the name of comb may be 

 given. One is composed of a sheet of chitin with a 

 number of slits and teeth and resembles a true comb. 



