152 THE I NTEGU MENTAL SKELETON OE THE IMAGO. 



This palp has frequently been mistaken for the antenna. 

 The true antenna is three-jointed, with a large terminal joint, 

 closely resembling that in the Muscidse. It lies in a groove 

 behind the simple eye. This position of the antenna is a 

 clear indication that the simple eye in the Fleas is not homo- 

 logous with the great compound eyes of insects, which are 

 never in front of the antennae. Its situation at the root of the 

 palpigerous blade of the maxilla apparently shows that it is 

 more nearly related to the maxillary eye-like organs of the fly 

 larva (see page 71). 



The inner proximal edge of the palpiger consists of a strong 

 sclerite (Fig. ■^^, a a), which articulates with a socket in the 

 peristome below and supports the lacina above. It is the 

 hinge of the maxilla, and it gives off a curved process (g) in 

 front, to which the margin of the sheath or pseudolabium is 

 attached. 



The pseudolabium frequently resembles and has been 

 described as a pair of palpi. This arises from the great 

 transparency of the ventral part of the organ. When properly 

 separated and prepared, the nature of the part is unequivocal, 

 and it agrees in every detail with the four-jointed sheath of the 

 hemipterous mouth. I regard this sheath as formed by the 

 united galeae of the maxilla. I have already drawn attention 

 to the palpiform character of the galea in Cicindela, so that the 

 resemblance of this sheath to a pair of united palpi, similar 

 to the labial palpi of the Hymenoptera, cannot be a valid 

 argument in favour of its being formed by the union of a 

 pair of labial palps ; and its connection with the base of the 

 maxilla indicates sufficiently its true character. 



Between the hinge sclerites of the maxillae a median prolon- 

 gation of the peristome (Fig. 33, /;) supports the curious 

 tubular ligula ; these are the only representatives of the lower 

 lip — labium — and the labrum as a distinct projection of the 

 peristome is entirely absent in all the Pulicidae. 



Great differences of opinion exist as to the nature of the 

 mouth organs in these remarkable insects. Taschenberg,* the 

 * Taschenberg, Otto, ' Die Fliihe,' 8vo, Halle. 1880. 



