172 
Larvae of Fleas 
this somite are the smallest of the ring, and there is a gradual increase 
in length as one follows the series upwards (Fig. 4 a). 
The tenth abdominal somite is very much smaller than the others, 
and the arrangement of the hairs is peculiar. A back view shows the 
anus a little above the centre, and below this is a pair of mounds carrying 
the struts or anal processes (Fig. 4 b). The mounds bear a number 
of fine hairs, and there is a more or less semi-circular row of fine hairs 
above the anal eminence, constituting the anal comb. 
The anal processes or struts are used in rapid progression to prevent 
any backward slipping of the body, but they are not hard claws as theif 
shape might suggest; the chitinous covering is pale and flexible, and 
the processes may be to some extent tactile in function. When viewed 
from the side the struts are slender, curved, tapering, and pointed at 
B 
Fig. 5. Anal struts of flea-larvae seen from the left side ( x 100). W. G. It. 
A, Ceratophyllus fasciatus ; B, Pulex irritans. 
the extremity in Pulex irritans (Fig. 5 b) and Ctenocephalus canis, 
and they are longer in Pulex irritans than in Ctenocephalus canis ; in 
Xenopsylla cheopis they are slightly thicker, less curved, and blunter 
(Fig. 4 a, a.s.). In Ceratophigllus fasciatus (Fig. 5 a), Ceratophyllus 
gallinae and Leptopsylla musculi the struts are thick, nearly straight, 
and blunt at the ends ; they are smaller in Leptopsylla musculi than 
in the two species of Ceratophyllus examined (see Table IV). It is 
of interest to note that in Pulex irritans, Xenopsylla cheopis and Cteno¬ 
cephalus canis the anal struts are straighter, blunter and less tapered 
in a newly-hatched than in a full-grown larva. 
The anal comb in Xenopsylla cheopis (Fig. 4, a.c.), Pulex irritans 
and Ctenocephalus canis consists of a single semi-cylindrical comb of 
about 22 fine straight hairs, arranged parallel with one another in very 
regular series, and the series is continued below in the form of two or 
three pairs of larger hairs set at wider intervals apart. In Pulex irritans 
these ventro-lateral hairs are as many as five pairs (Table IV). In 
Ceratophyllus fasciatus, Ceratophyllus gallinae and Leptopsylla musculi 
the anal comb has a more ragged appearance, which is due to the fact 
that the comb is double, consisting of a principal comb of about seven 
