4 o THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Now, the great resemblance between the claspers of P. irritans, leporis and the 
Sarcopsyllids in contradistinction to the dissemblance between the claspers of P. irritans 
and those of the other Pulicidae is surely highly convincing evidence of the correctness 
of our contention that the Sarcopsyllids are closely related to P. irritans. 
The clasper of the Sarcopsyllids offers some interesting specific and generi : 
differences, the three genera Dermatophilus, Hectopsylla, and Echidnophaga having each 
distinctive features in this organ. The manubrium of the clasper is longitudinal in 
direction in D ermatophilus and Echidnophaga (PI. Hand III, Fig. 18-22), while it isvertical 
and very short in Hectopsylla (PI. II, Fig. 1 6 and 1 7). The dorsal portion of the segment 
bearing the sensory plate is almost completely separated from the clasper in Dermato- 
philus and Hectopsylla. In Echidnophaga the segment is much wider in the dorsal line 
than above the manubrium (apart from the processes of the clasper), while in Hecto- 
psylla the clasper is widened frontad, the small manubrium projecting downward from 
the lower anterior angle. There is in Hectopsylla a second small manubrium projecting 
upward from the upper corner of the dilated part. The processes vary much in size 
and shape in the different species (compare PI. II and III). 
The ninth sternite of the Siphonaptera has generally the shape of a boomerang in 
a lateral view, the internal arm being subvertical, extending from the clasper down- 
ward, and the external or ventral arm being more or less horizontal. The two 
' boomerangs ' of the two sides of the body are either entirely separate, or they are 
connected with one another at the angle, or the horizontal parts are completely united. 
In the Sarcopsyllidae the ninth sternite has this boomerang shape in Echidnophaga. 
In D ermatophilus the sternite is represented by a rather broad, elongate, horizontal 
plate on each side (Fig. F). The ventral portion of the sternite is also in Hectopsylla 
much wider than in Echidnophaga. The distal part of this ventral portion protrudes 
in Hectopsylla beyond the apex of the eighth sternite, forming a large flap which has 
the appearance of being articulated with the eighth segment (PI. II, Fig. 17 and 18). 
Both in Dermatophilus and Hectopsylla the vertical portion of the ninth sternite is 
apparently represented by an internal incrassation on the eighth sternite. 
In the % it is the eighth segment (PI. I and II, Fig. 9-15) which has undergone 
modifications for sexual purposes, and sometimes also the seventh sternite, the latter 
especially often in Ceratophyllus and Ctenophthahnus. The seventh sternite is simple 
in the Sarcopsyllids as it is in Pulex irritans and most other members of the genus 
Pulex. The tergite aud sternite of the eighth segment were originally doubtless of 
nearly equal size, as in the preceding segments. In the Sarcopsyllidae as in many other 
Siphonaptera the tergite has become much enlarged, while the sternite is reduced to a 
very small plate. The tergite is in the Sarcopsyllidae completely divided in the mesial 
line. 
The dorsal portion of the ninth tergite in Siphonaptera is practically identical in 
the two sexes. The sensory plate differs in Hectopsylla and Dermatophilus very essen- 
tially from that of Echidnophaga. The bristle-bearing grooves are separated in the 
