A. W. Bacot AND W. Gr. Ridewood 
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of Xenopsylla cheopis (Fig. 6) the plates are lightly outlined. The 
various plates can be well seen in a moulted skin, and are particularly 
distinct in the larvae of Ceratophyllus yallinae. 
The thinner parts of the cuticle appear soft, smooth and glistening, 
but under a high power of the microscope they exhibit a peculiar pattern 
like a fine honey-comb or a shagreen. This pattern is due apparently 
to slight elevations of the surface, for in Ceratophyllus yallinae the 
surface is definitely raised into close-set rows of backwardly directed, 
blunt spikes, like the teeth of a coarse rasp. In the more ventral parts 
of the body the spines are blunter and rounder, and more like those of 
the larvae of the other species, though coarser. These elevations are 
not present on the dorsal and other plates of the body, where the chitin 
is thicker and yellower. 
The hairs or setae of the body somites are disposed in more or less 
transverse rows or rings, and consist of a ring of large hairs near the pos¬ 
terior edge, and a ring of smaller hairs in front of it. The regularity 
of the rings of small hairs is disturbed in the vicinity of the stigmata, 
which occur laterally in the first thoracic somite and the first eight 
abdominal somites. The tracheal system is best studied by drowning 
a larva in 50 % alcohol. The main tracheae consist on each side of a 
double longitudinal trunk, linked together in the anterior third of each 
segment by a fine tube. The stigmata are the minute openings of very 
slender tubes which extend to the surface from the middle of these links. 
The right and left lower longitudinal tubes are connected by transverse 
ventral tubes in the middle of the length of each segment. Laboulbene’s 
figure (1872, PL XIII, Fig. 13) is good, except that he shows a stigma on 
the third thoracic somite. The stigmata lie at the edge of the lateral 
plate, antero-dorsally to the base of the upper lateral large hair ; each 
stigma is on the lateral elevation of the body, and has three of the 
finer or anterior hairs disposed around it. 
Each of the large hairs arises from the middle of a small circular 
area of soft and flexible chitin, and in certain positions there are to be 
found similar circular areas with no hairs arising from them. These 
last are more noticeable in the larvae, of Xenopsylla cheopis and Pulex 
irritans than in those of Ceratophyllus fasciatus and Ceratophyllus 
yallinae. 
The arrangement of the long hairs on the dorsal plates varies in 
different species, and may in conjunction with other characters be used 
to distinguish cast skins of larvae. The skins should be softened in 
warm water or 50 % alcohol, and spread out on a slide, Of the six 
Parasitology vu 12 
