87 



in the diptei'a, witli which the fleas are usually allied. The head is 

 ■divided into two nearly equal parts by the antennary groove, in front 

 of which are placed the eyes (when these are present) and the oral 

 appendages. The eyes are simple, and normally appear as dark brown 

 or black spots close to the antennary groove and towards the lower side 

 of the head. On the side of the head are seen several chitinous hairs, 

 which from their position and size in different species form useful specific 

 i;haracters. These are used in assisting the insect to obtain a strong 

 hold on the skin of its host. 



The oral appendages are adapted for suction and consist of a pair 

 of free plates and a tube made up of five separate pieces. 



The free plates are the maxillae, and are usually triangular in 

 outline and of a dai-k chitinous colour. Each maxilla bears at its base 

 -a four-jointed palps, the joints of which are of different lengths in the 

 different species, and are partly covered with fine hairs. These ai'e the 

 organs which were by old observei's taken for the antenniB. 



The peculiar sucking tube is formed from the lower lip or labiiim, 

 the mandibles and an impair piercing tube or lingua. 



The labium is impair at its base, then bifu.rcates, dividing into two 

 four-jointed palps, each of which is hollowed out on the inner side. On 

 the upper side this palp is thick, but it thins out and becomes mem- 

 braneous on the lower sidt>, being in shape somewhat like the blade of 

 a hollow ground razor. These two half tubes lie together and enclose 

 the mandibles and the lingua. 



The paired mandibles are long, narrow, longitudinally ribbed, and 

 are also deeply excavated along the inner side, while the borders, except 

 at the base, are strongly serrated, the teeth becoming more prominent 

 towards the outer end. 



In the tube formed by the mandibles, which are generally pressed 

 close together, lies the suctorial organ, or lingua, in the form of a flattened 

 needle, coarsely serrated on the uj^per border and traversed by a narrow 

 canal, along which runs a very slender trachea or air-tube. At its 

 ■hinder end it enlarges into a rounded sac before opening into the 

 oesophagus. This organ is considered by some as representing the 

 upper lip or labrum, but, on account of its mode of insertion rather 



