REVISION OF THE SARCOPSYLLIDAE 39 
Sipbonaptera. The clasper of Pulex irritans bears distal ly three separate processes, 
each being moveable by itself, there being a suture (or joint) between each process 
and the main body of the segment. The upper process (Fig. E, P') is broad in 
P. irritans and hairy. The second and third processes (P 2 and F) are much 
smaller, and form together a kind of claw reminding one of the pinchers of a lobster, 
the upper process (P 2 ) being slightly curved downwards, and the lower process 
(F) upwards. The lower process is longer proximally than the upper, extending 
much further proximad. 
These three processes, of which the two lower ones form a pair of pincers, occur 
in a similar shape only in Pulex leporis (= goniocephalus) among the Pulicidae and 
Ceratopsyhidae. The allies of Pulex pallidas {cleopatrae, nubicus, isidis, etc.) have also, 
three processes, but the two lower ones have completely lost their pincer-like appear- 
ance, while there are never three free processes in any other Pulicid or Ceratopsyllid. 
On the other hand, the processes of Pulex irritans and leporis are found again in the 
Sarcopsyllidae, the resemblance being very close indeed between these organs in Pulex 
irritans and in the species of Echidnuphaga and Hectopsvl/a, as will be seen by comparing 
Fig. E. and Fig. 16-22. The genus Dermatophilus has also preserved the pair of 
pincers, but the upper process of this pair is fused together with the main body of the 
clasper, there being no suture separating this process (Fig. F). The dorsal process 
(P 1 ) moreover, found in the other Sarcopsyllids as in Pulex irritans, has become 
completely lost. The state of development of the various portions of the claspers of 
Dermatophilus throws some light on the homology of the various parts of the clasper 
in those Sipbonaptera which do not possess the three separate processes found in Pulex 
irritans. As there is doubtless a close phylogenetic connection between Pulex irritans 
pallidus, etc., and the other genera of Pulicidae, it may be asked what has become of 
the three separate processes found presumably in the ancestral forms of those Pulicidae 
and the Ceratopsyllidae which have only one free process, the so-called ' Finger ' ? 
One point offers no difficulty whatever. A comparison of the claspers of the various 
Siphonaptera shows at once the homology of the lowest process (F) of P. irritans and 
the Sarcopsyllids with the ' Finger,' which is articulated to the clasper. The second 
process (P 2 ) of P. irritans is in the other Pulicids merged together with the main 
body of the clasper, as in Dermatophilus penetrans (Fig. F), forming usually a more or 
less slender projection which has sometimes preserved an appearance similar to that 
found in Pulex irritans, for instance in some of the Ceratopsyllidae. The uppermost 
process (P 1 ) has either become completely lost, or it has become reduced and like 
the middle process merged together with the clasper. In Ceratophyilus hilli the articu- 
lation between the finger and the clasper has also disappeared (Nov. Zool. xi. t. 11. 
Fig. 43). In Ctenocephalus canis and felts the uppermost process is vestigial, the middle 
process has developed into a rather large flap, and the lowermost, though shortened, 
has preserved a shape resembling the same process of P. irritans. 
