26 
The Non-Combed Eyed Siplionaptera 
beneath it, projecting a little below, the epimerum. This stigma, or 
rather the walls of the cavity in which the trachea opens, is nearly 
globular, appearing in a lateral view to be situated on a short stalk, 
the whole being cup-shaped (PI. II, fig. 1, sti). This organ was formerly 
often mistaken for a remnant of the mesothoracic wing, though the 
vestige of wings, if there are any vestiges left in any Siphonaptera, 
should be sought for in the place where the wings of insects are inserted, 
namely, between the sternite and tergite, i.e. dorsally of the epimerum 
and not ventrally of it. The mesosternite has always some bristles on 
the side, there being usually one at the internal incrassation, two at 
the stigma and one further dorsal, some species (for instance regis and 
chephrenis) having one or two more bristles. 
The metanotum is sometimes shorter, and sometimes longer than 
the mesonotum in Loemopsylla, but the metasternite on the other hand 
is always larger than the mesosternite, the great development of the 
metathoracic epimerum being quite a special feature of the Siphona¬ 
ptera. The metasternite has preserved the original sutures dividing 
it into three main sclerites, the fusion not having proceeded so far as in 
the case of the mesosternite. The meral suture is quite plain (see 
diagram, figs. A and B), and the anterior portion is again clearly divided 
by a horizontal suture into a sternum which is ventral, and an 
episternum which is lateral. The episternum is in Loemopsylla smaller 
than the sternum. It varies, however, a good deal, being, for instance, 
much longer in L. longispinus than in the other species of this genus. 
The most interesting feature in connection with this episternum of 
Loemopsylla is the more or less complete fusion with the sternum which 
obtains in a number of species, the suture between the two sclerites 
partially or totally disappearing both externally and internally in 
several species. In these species, therefore, the metasternite agrees 
more closely with the mesosternite than in the other species with 
a separate metathoracic episternum. This specialization we have found, 
outside the genera which are the subject of this paper, in an American 
Ceratophyllus 1 only. The fusion does not occur in the American 
non-combed Puliciclae, but is found in Pulex irritans and to a certain 
extent in the Old World species Ctenocephalus erinacei and Spilopsyllus 
cuniculi. The third sclerite of the metasternite is the epimerum, which 
extends from the first abdominal tergite downwards to the hindcoxa, its 
1 Ceratophyllus terinus Bothsch (1905). In our revision of the Sarcopsyllidae, we 
stated (1906, p. 30) that the epimerum and sternum of the metathorax are fused as in 
Ceratophyllus charlottensis. This was a pen-slip for C. terinus. 
