vi] CHIGOES AND THEIR ALLIES 79 



extent of forehead which can be pressed against the 

 skin of the host the less the strain on the upper lip 

 and mandibles, which serve as anchors, when the host 

 scratches. 



All the chigoe family have eyes ; but in one 

 recently discovered species the eye is very small 

 and devoid of pigment. Like those of other fleas, 

 the antennae fit into grooves at the side of the head, 

 and the club, which is the sensitive part of the organ, 

 consists of eight segments. In a good many fleas the 

 antennae are different in the two sexes, but there is 

 no obvious sexual distinction in this family. 



The peculiar development of the mouth-parts is 

 one of the most singular features in the structure 

 of the chigoes and their relatives. These important 

 organs are modified in a fashion not to be found in 

 any fleas outside the family. Here, as in other fleas, 

 the mandibles are piercing organs which penetrate 

 the skin of the host, the upper lip serving in con- 

 junction as a sucking tube. In ordinary fleas these 

 organs are retracted when the insect has done its 

 meal ; in the present family they remain, in the case 

 of the females, apparently permanently fastened in 

 the skin. The piercing organs are broader and the 

 serrate edges of the mandibles more solid and heavy 

 in this family than in the case of other fleas. 



The two methods by which fleas keep in touch 

 with their hosts have already been alluded to. The 



