162 
Larvae of Fleas 
observations 1 , however, show that Defrance’s argument is not sound, 
for when a flea is in a gluttonous mood, it discharges, not small grains 
of uniform size, but drops of red, liquid, and scarcely digested blood. 
These drops and splashes will on drying assume irregular shapes little 
suggesting that they are anal discharges. 
In rearing the larvae of fleas it is essential that the atmosphere should 
be of the right degree of humidity; the material (sawdust, sand, etc.) 
in which they are kept should not be wet, on the other hand the larvae 
soon shrivel up if the air is too dry 2 . 
Structure oe the Head. 
The head of the larva has a thicker chitinous covering than the other 
parts of the body, and appears yellower or browner in colour. The size 
and shape vary in the different species—in Xenopsylla cheopis the head 
is small and tapers considerably in the front part when viewed from 
above, whereas in Ceratophyllus fasciatus and Ceratophyllus gallinae 
the head is large and rather oval when viewed from above (see Figs. 
1 and 2). Intermediate between these two extremes are the heads 
of Pulex irritans and Ctenocephalus canis, both of which are narrow in 
the snout, but less distinctly so than that of Xenopsylla cheopis. The 
head of Pulex irritans is larger than that of Ctenocephalus canis, and the 
head of Ctenocephalus canis is larger than that of Xenopsylla cheopis. 
The head of Leptopsylla musculi is of the same shape as that of Cerato¬ 
phyllus fasciatus, but it is rather smaller. 
The mouth is nearly terminal, in the lower half of the head ; the 
most anterior part of the whole head is the upper lip, or labrum, a soft, 
thin flap which is nearly straight and horizontally disposed, or has the 
sides bent down, according to the action of the muscles of the mouth. 
Projecting sideways from the head, and slightly upward and forward, 
are the two antennae, and projecting forwards, sideways, and slightly 
downwards are the maxillary palps. The labial palps are very small, 
situated near the ventral median line of the head, at about one-fourth 
or one-third of the length of the head from the front. Except for the 
antennae, and the maxillary and labial palps, the only projections 
1 See results of experiments on the rearing of fleas by A. W. Bacot, Journal of Hygiene, 
Plague Supplement in. Jan. 1014, pp. 466-467, 471-472, 499-500, 513-517, 646-647. 
2 For recent observations on the influence of temperature and humidity upon the 
rearing of larvae see A. W. Bacot, Journal of Hygiene, Plague Supplement in. Jan. 1914, 
pp. 513-533, 646-647. 
