THE AIR SAC MITE OF THE FOWL. 
13 
a short bristle directed outward and forward, while at the tarsus 
at the base of the ambulacral sucker, there at times appears to 
be another hair or projection which is probably rather a folding 
of the chitinous covering oi the foot. The second pair of legs 
(Fig. d) shows in addition to these hairs, an elongated retractile 
spur, pointing upwards and backwards from the tarsus, at right 
angles with it, about as long, though not as thick, as the ambu¬ 
lacrum. The epimera of the first pair unite on the median 
line to form a triangular sternite ; the apex directed backwards, 
the base occupied by the rostrum. The epimera of the second 
pair are free and slightly arched or sinuous. The two posterior 
pairs of legs are large, glabrous and almost as strong as the two 
anterior pairs, their epimera free and arched, the convexity 
being forwards, and each showing near its base a short spur-like 
projection, extending forwards ; the coxae very large, globular. 
Anus hypo-marginal. 
The ovigerous female (Figs, a and d) varies in size from 
.45 to .66 m.m. long, and .38 to .55 m.m. wide. The vulva is 
between the epimera of the two last pairs of legs, extending for¬ 
ward almost to the epimera of the second pair, and consists of a 
longitudinal cleft, wider in front than behind, and furnished on 
either side at its anterior third with a short obtuse prolongation 
inclined backwards and outward like the barbs of a harpoon. 
Within the transparent body there is always observable two 
to twelve ova in various stages of development, one to six or 
seven of which contain six-legged larvae (Figs, d and d), the legs 
readily distinguishable folded on the ventral surface of the 
body. By slight pressure on the cover glass the larvae can be 
pressed out of the female and show after their extrusion ener¬ 
getic movements. 
The parasite deposits no eggs, but gives birth to living 
young, is ovo-viviparous, and the extreme variations in size, as 
noted above, are due to the number of ova contained within the 
body. 
The male is .45 to .50 m.m. long, and .38 m.m. wide, pre¬ 
senting on the middle of the ventral surface a well-marked 
