22 
The Non-Combed Eyed Siphonaptera 
frons and is situated between the antennae. In the $ the groove does 
not extend nearly so far dorsad and the internal incrassation is absent 
or vestigial only. The antennae themselves show a corresponding 
difference in the sexes, being longer in the </ than in the $, as is 
generally the case in fleas. The first segment especially is very much 
longer in the J 1 of Loemopsylla than in the $, the difference between 
the sexes being much slighter in the American forms. The second 
segment is transverse and bears in both sexes a row of long bristles at 
the apical edge. These bristles are longer in the $ than in the <£. 
The club is somewhat shorter in the $ than in the </• The nine 
segments composing it are separated on the posterior side 1 by the 
segmental incisions, the incisions being especially deep between the first 
four segments. The anterior side of the club is solid, only three central 
incisions being faintly indicated. On the inner surface the club bears 
very numerous minute hairs in the </ only. The bristles of the head 
are likewise not quite the same in the sexes, inasmuch as there is in 
the along the hinder side of the antennal groove a row of small hairs, 
which is represented in the $ by a very few hairs only. These hairs 2 
of the are not placed very close together, the interspace between 
every two being at least equal to one-fourth the length of the hairs. 
In this character the £ £ of Loemopsylla differ from the American 
Pulicidae of the present group of genera, the hairs being very close 
together in the f of the American forms and also numerous in the 
$ $ (PI. II, figs. 3, 12). The function of these short stiff hairs may be 
simply protective. The antenna is an organ of smell which plays an 
important sexual role, inasmuch as it enables the sexes to find each 
other, and might easily be injured if it were exposed 3 , when the flea is 
gliding through the fur or feathers of the host. The antenna is protected 
by being enclosed in the antennal groove, of which the anterior edge 
often partly projects over the groove. Possibly the row of short hairs 
at the posterior side of the groove may protect the antenna from behind. 
The hairs, however, may also serve as a kind of comb for cleaning the 
antenna, insects generally having some means or other (forelegs, mouth- 
parts) with which they are able to remove dust or dirt from this organ 
of sense. In Rhopalopsyllas they are placed on a carina (PI. II, fig. 3). 
The other bristles of the head are practically alike in the sexes. 
1 “ Posterior” when the antenna is lying in the groove. 
2 Dahl (1898, p. 191) calls these bristles the remnants of a faceted eye. 
3 The antennae of s s when in copula are usually exposed; further observations on 
this point would be interesting. 
