A. W. Bacot and W. G. Ride wood 
165 
smaller, hemispherical processes. In Pulex irritans, Xenopsylla cheopis 
(Fig. 1, a.p.), and Ctenocephalus canis the three large processes are shaped 
like teats or projectiles (type A), but in Ceratophyllus fasciatus (Fig. 2, 
a.p.), Ceratophyllus gallinae and Leptopsylla musculi they are pointed, 
and have the form of rather long cones (type B). 
Mandibles. 
Although adult fleas are provided with piercing and sucking mouth- 
parts, and live on blood, the larval forms are not parasitic, and have 
mouth-parts adapted for biting and nibbling. The mandibles, though 
doubtless they project from the mouth during feeding, cannot in a dead 
specimen be seen without dissection, or making the head transparent 
(by dehydrating and clearing with xylol, or by the action of a 15 % 
solution of caustic potash for three days), when they can be seen by 
reason of their being darker in colour than the other parts of the head. 
A B C D E F 
Fig. 3. Mandibles of Larvae of Fleas ( x 300). W. G. R. A, Pulex irritans ; B. 
Xenopsylla cheopis ; C, Ctenocephalus canis ; D, Ceratophyllus fasciatus ; E, Cerato¬ 
phyllus gallinae; F, Leptopsylla musculi. All drawn by camera lucida with 
apochromatic objective 4 mm. and compensating ocular No. 4, and subsequently 
reduced to three-fourths ; it is to be noted, however, that in different full-grown 
larvae of the same species the mandibles vary considerably in size. 
The front part of each mandible is strongly chitinised and ends in 
a tooth, which is nevertheless more or less in series with the lateral 
teeth. The mandibles are disposed with their points directed forwards, 
and their concave faces towards one another. The large terminal tooth 
is the lowest of the series, and the other teeth are set along the antero- 
dorsal edge for about one-fourth ( Pulex irritans), one-third ( Cerato¬ 
phyllus fasciatus), or one-half ( Xenopsylla cheopis) of the total length 
of the mandible. 
