A. W. Bacot AND W. Gr. Ridewood 
171 
The large hairs of the larva of Pulex irritans are much paler and 
shorter than those of the other species investigated ; they are blacker 
in Xenopsylla cheopis than in Ceratophyllus fasciatus and Leptopsylla 
musculi. In Ceratophyllus fasciatus and Leptopsylla musculi the dorsal 
hairs on abdominal somites 7 and 8 are considerably longer than those on 
somites 5 and 6, and those on somite 9 are longer still ; i.e. the posterior 
hairs of the dorsal half of the body increase in length gradually from 
abdominal somite 1 to somite 9. In Xenopsylla cheopis, on the other 
hand, they increase in length more gradually from abdominal somite 1 
to somite 8, and those of somite 9 are considerably longer. In other 
Fig. 4. Hind end of a larva of Xenopsylla chenopis ( X75). W. G. R. A, left side view 
of tlie last two somites ; B, back view of the anal somite (abdominal 10) with the 
hairs represented as though cropped short. 
a. anus ; a.c. hairs of the anal comb ; a.s. anal strut. 
words, the dorsal hairs of abdominal somites 7 and 8 are in Ceratophyllus 
fasciatus and Leptopsylla musculi much longer in proportion to those 
of somite 9 than they are in Xenopsylla cheopis. In Ctenocephalus canis 
the dorsal hairs on abdominal somites 7 and 8 are scarcely longer 
than those on somites 5 and 6, and those on somite 9 are not nearly 
so long in proportion as they are in Ceratophyllus fasciatus, Leptopsylla 
musculi and Xenopsylla cheopis. The dorsalmost pair of hairs on the 
ninth abdominal somite is the longest in the whole body of a larva, 
and extends straight backward, instead of radiating in series with the 
other large hairs of this somite (Fig. 4 a). The ventralmost hairs on 
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