24 
The Non-Combed Eyed Siphonaptera 
loss of bristles in Loemopsylla and the allied Old World genera is not 
a consequence of the reduction of the segments in width, but indicates 
rather the general tendency towards reduction obtaining in many organs 
of these Old World Siphonaptera. The pronotum of Loemopsylla never 
bears a comb, nor are there any slender, bristle-like, subapical spines on 
the mesonotum, nor has the metanotum ever a dentate or serrate apical 
edge. 
The sternites of the thorax, with the exception of the prothorax, 
have preserved the original main division into an anterior and a 
posterior portion. The prosternite, as is very often the case in insects, 
does not show any distinct separation into several sclerites. It bears 
the coxae at its anterior corner, the whole prosternite therefore being 
postcoxal. The lateral portion of the prosternite, which is larger, 
especially in length, than the ventral portion, has in Loemopsylla the 
same shape as in Pulex, being widest near its hinder end. It is strongly 
chitinized beneath, being more or less flattened behind the coxae. The 
meso- and metasternites on the other hand are ventrally membranaceous 
from the insertion of the coxae backwards. The prosternite never bears 
any bristles in Siphonaptera, which is remarkable, since the meso- and 
metasternites have quite a number of bristles on the sides. Above the 
slanting posterior edge of the prosternite is the first stigma, situated 
between the prosternite and the protergite and concealed underneath 
the overlapping edges of these sclerites. In a mounted (cleared) 
specimen the circular trema of the stigma and the trachea are generally 
plainly visible (PL II, fig. 1). 
The mesosternite exhibits a similar characteristic reduction in size 
and shape as in Pulex. There is, however, in Loemopsylla, as in the 
other Pulicidae, a rod-like internal incrassation laterally in the 
mesosternite, extending from the insertion of the coxa upwards and 
corresponding to the meral suture of other insects, which divides the 
sternite into an anterior (= sternal) and a posterior (= meral) portion 
(see diagram, figs. A and B). The meral suture itself is absent from 
the outer surface of the sternite in Loemopsylla. This internal rod-like 
incrassation is absent from Pulex and the Sarcopsyllidae. From the 
insertion of the coxa forwards there is another internal incrassation 
which corresponds to a suture separating in other insects the sternum 
from the episternum. The most anterior portion of the mesosternite of 
Loemopsylla is therefore homologous to the sternum, and the triangular 
portion situated further dorsal homologous to the episternum. The 
relative position of these two sclerites, which are entirely fused in 
