Nycteribiide, parasitic Diptera, from Ceylon. 423 
are large, and bear the very long and strong fuscous-reddish bristles. 
It appears that Enderlein* had some doubt as to the number of 
these bristles, as Westwood’s Fig. 3+ does not show clearly whether 
one or several rows are present. It may be stated that there are 
5 or 6 rows, not very regularly arranged, and behind them a narrow 
part of the segment without either bristles or tubercles. There is 
no apparent arrangement of the tubercles in definite transverse 
lines, such as is mentioned by Westwood. 
Terminal segment. The chitinous plates on either side of the 
anus are smooth, dark, and shining; each one bears on its free 
margin a row of 8 long and very strong dark bristles, and 
immediately within this outer row is an inner row of very fine short 
bristles. The plate covering the genital opening is slightly broader 
than long ; smooth, brown and chitinous, bearing short bristles ; the 
centre of its basal portion is whitish, and of the same soft consistency 
as the penultimate segment. The margin of this plate has a slight 
median emargination, on either side of which it bears a row of about 
8 short black teeth, forming a kind of ctenidium.§ 
The females vary greatly in appearance according to 
the period of gestation, as often noticed previously. ‘Those 
in a less advanced stage have the abdomen greatly con- 
tracted, the posterior bristles lie together projecting back- 
wards, the black tubercles on the integument are crowded 
together, and the ctenidium can be seen from above widely 
projecting on either side of the body. Such females 
sometimes measure only 44mm. in length. Those in an 
advanced stage have the penultimate abdominal segment 
much swollen, with a marked constriction just behind its 
base; the long posterior bristles are erected, the black 
tubercles at some distance from one another owing to 
expansion of the integument; and the ctenidium is hardly 
visible at the sides of the body from above, since the 
hardness of the basal ventral plate prevents it from sharing 
in the expansion of the rest of the abdomen. Gravid 
females such as these measure 5 mm., or over, in length. 
VARIATION IN THE FEMALE. When allowance is made 
for difference in appearance due to difference in the stage 
of gestation, the 43 females are remarkably constant in 
almost all their characters. The only appreciable variation 
which has been found, is in the number and arrangement 
* loe, cit. al ft op. cit. £ op. cit., p. 283. 
§ These ctenidia are present also in our 9 specimen of 0. 
horsfieldi. 
