A. W. Bacot and W. G. Ridewood 
159 
as if of pure white wax or china, being slightly translucent, with a smooth, 
polished surface. 
Newly hatched Larva. 
The larva on hatching is small, slender and semi-transparent, with 
sparse but regularly disposed hairs. It consists of a head, three thoracic 
somites and ten abdominal somites, the last being much smaller than 
the ninth, and provided with a pair of downwardly and backwardly 
directed processes, the anal struts. On the top of the head of a newly 
hatched larva is a curious egg-breaker, by means of which a slit is formed 
in the egg-shell through which the larva emerges. This egg-breaker, 
first described by Kiinckel (1873, p. 135) in the larva of Ctenocephalus 
fells and Ceratophyllus fasciatus, although previously noticed by Roesel 
and De Geer, seems to be regularly present; it has been observed by 
Bonnet (1867) in Sarcopsylla penetrans, and by Packard (1894, p. 318) 
in Ctenocephalus canis, and by ourselves in Pulex irritans, Xenopsylla 
cheopis and Leptopsylla musculi, while its presence in larvae of Cteno¬ 
cephalus fells is confirmed by Balbiani ( Comptes rendus 1875, p. 904), 
and in those of Ctenocephalus canis and Ceratophyllus fasciatus by 
ourselves. The egg-breaker consists of a more or less pyriform structure, 
lying in a depression on the upper surface of the head. The upper 
ridge, which ends in front in the small sharp tooth, is more strongly 
chitinised than the other parts, and the organ gives one the impression 
of being capable of inflation and upward extension so as to press the 
tooth into the inner surface of the egg-shell. Kiinckel notes (p. 136 
and Figs. 2 and 3) that the tooth of the egg-breaker is set farther back 
on the organ in Ceratophyllus fasciatus than in Ctenocephalus felis. No 
trace of the egg-breaker is to be seen in larvae after the first moult. 
Growth of the Larva. 
A newly hatched larva is more cylindrical, i.e. of more uniform 
width, than one of larger size. As the larva grows the fore and hind 
ends assume a more tapered form ; the tapering of the front end is a 
gradual one from the eighth abdominal segment to the head ; the taper¬ 
ing of the hind end, from the eighth to the tenth abdominal segment, 
is more abrupt. The head does not increase in size at the same rate as 
the other parts of the body, and so an older and consequently larger 
larva has a relatively smaller head than a small larva, and the front 
portion of the body appears more pointed. 
