FAMILY SARCOPSYLLIDAE 447 



The Sarcopsyllidae are regarded by Jordan and Rothschild as 

 connected with the Pulicidae, the central family of the order, 

 partly by convergent development and partly by blood relationship. 

 The females, to a varying extent in the different genera, have the 

 characteristic habit of fixing themselves to the skin of the host, and 

 remaining attached in one position for the greater part of their existence, 

 after the manner of ticks ; the modifications of external structure which 

 are associated with this habit may be so marked that, in the extreme 

 case of the 'Jigger', all outward resemblance to the other fleas is lost 

 when the female is far advanced in pregnancy. The jigger has, in fact, 

 been mistaken for a mite. 



The most striking features are to be found in the head, and show 

 how the insect has become adapted so as to be able to fix itself to its 

 host by means of the mouth parts. The mandibles (Plate LIV, fig. 1) 

 are very much larger and more heavily serrated than are those of the 

 Pulicidae, and recall in a striking manner the fixing mouth parts of ticks. 

 The labium is much thinner and less chitinized, and has the joints reduced 

 to two or three. According to Jordan and Rothschild this is ' in conse- 

 quence of the females fixing themselves permanently on the host by means 

 of the mandibles and upper lip.' The mouth, instead of pointing down- 

 wards, as in the Pulicidae, is directed more forwards, the frontal angle not 

 projecting ventrally. This has brought about a corresponding alteration 

 in the shape of the head, the dorsal border being shortened, and in many, 

 as in Echidnophaga gallinaceus, almost flattened in front ; the dorsal and 

 the anterior margins meet at an angle, which may be marked by a depres- 

 sion with a tubercle on each side, or by a thickening of the chitin. 



It is characteristic of the group that the genal angle of the head is 

 produced to a hook-shaped process, known as the post-oral process. 

 This takes the place of the genal comb, and assists the flea in maintain- 

 ing its hold upon the host. 



The thorax is modified in a very characteristic manner, by the shorten- 

 ing of the: sclerites which compose the wall until they are together 

 shorter than the first abdominal tergite. The effect of this is to allow 

 of: much: .freer expansion of the abdomen in the female, and to render the 

 insect less liable to be detached from its host. The abdominal sclerites 

 in the male and in the undistended female do not differ much from those 

 of the Pulicidae, but in the pregnant female the normal relations of the 

 parts are greatly altered, and the sclerites separated from one another, 

 . .The. legs, as one would expect, are only feebly developed, and 

 the claws are small, for the insect does not need them in . its 



