26 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
its allies. ~D ermatophilus has seldom as many as four hairs similarly placed. These 
hairs are completely lost in Hectopsylla. There is no obvious sexual difference in 
the antennae of the Sarcopsyllids as is so often the case in Pulicidae, especially in 
Ceratophyllus. The antennae, however, of Hectopsylla on the one hand, and Dermato- 
philus and Ecbidnophaga on the other differ somewhat in the shape of the club, the 
club being distinctly longer in Hectopsylla than in the other genera, Ecbidnophaga 
bradyta approaching Hectopsylla in this respect. 
One of the most singular features in the morphology of Sarcopsyllidae is the 
peculiar development of the mouth-parts. These organs are modified in a 
characteristic way not observed outside the family. 
Here, as in other Siphonaptera, the mandibles are piercing organs penetrating 
the skin of the host, the upper lip serving as a sucking tube. While in ordinary 
Siphonaptera these organs are retracted after sucking, they remain fastened in the 
skin, apparently permanently, in the case of the of the Sarcopsyllidae. The piercing 
organs of the Sarcopsyllidae are much broader, and the serration of the mandibles is 
much heavier than in the case of other fleas, including such fleas as Vermipsylla, 
Malacopsylla, etc., of which the are more or less stationary. The mandibles are 
widest near the base. Their enlargement in both sexes is connected wuh the method 
of fixation on the host. The Siphonaptera have two main organs of fixation, the 
legs and the piercing organs, the extreme developments of which are represented by 
Malacopsylla on the one hand, and by the Sarcopsyllidae on the other, and we observe 
accordingly two lines of development. In Malacopsylla we have comparatively weak 
and short piercing organs, while the claws and the bristles of the legs are very strongly 
developed, enabling the specimens to fix themselves firmly on the host. In the 
Sarcopsyllidae, on the other hand, the legs are practically useless for that purpose, at 
least in the more specialized forms, the bristles and claws being very thin. In this 
family the mandibles serve the purpose of the claws, the specimens ($$) being fixed 
on the host by means of these piercing organs. The legs oi the Sarcopsyllidae are often 
torn off and mutilated, doubtless by the host when trying to pick the parasites off. 
This being so, one might be justified to conclude that the strong development of the 
mandibles is a consequence of the assumption of a stationary life on the part of the 
the having inherited the same strong organs of fixation from the though 
the enlargement is unnecessary in this sex, not being stationary like the 
Among the Pulicidae the species which comes nearest to the Sarcopsyllids in the 
width of the mandibles and the strength of the serration is Pulex itritans. The 
mandibles are not of the same size in all the Sarcopsyllidae, being least enlarged in 
Hectopsylla coniger. In this species of Hectopsylla as well as in H. psittaci and broscus, 
the serration of the mandibles does not extend to the base. 
The maxillae are triangular, as in the Pulicidae. They vary a good deal in out- 
line in the different species. They are, for instance, long, sharply-pointed, and curved 
