L. E. Robinson and J. Davidson 
o 1 
01 
the ventral surface, is due the crenulated appearance of the posterior 
margin of the body in mounted specimens. The hairs, particularly 
those situated on the posterior portions of the body, are often slightly 
serrated, and in many cases the truncated tip is split into two, three or 
even more fine points. The supracoxal and coxal folds are barely 
developed. 
The Genital Orifice. 
Plate I, fig. 2 ; Plate II, fig. 4; and Plate III, figs. 3, 4 and 7. 
In both sexes the genital orifice is situated in the mid-ventral line, 
about the level of the first intercoxal space. Its position is subject to 
some slight degree of variation, particularly in the case of the female, 
in which it tends to move towards the basis capituli as the time of 
oviposition approaches. 
As already stated, the size and appearance of the genital orifice 
afford a ready means of distinguishing the sexes. 
The genital orifice of the female (see PI. Ill, figs. 4 and 7, gen.ap.) 
is a conspicuous, transversely placed slit with more or less tumid lips. 
The posterior lip protrudes so far as to just overlap the anterior lip, the 
margin of which is thus concealed when the aperture is closed. The 
actual opening is, in consequence, directed forwards towards the 
capitulum, an arrangement which is obviously associated with the 
remarkable process of oviposition. The posterior lip of the genital 
aperture is continued backwards without interruption into the post¬ 
genital area, the outline of which is roughly that of an equilateral 
triangle with a posteriorly directed, truncated apex. The cuticle of 
both genital opening and post-genital area is sufficiently pliable and 
extensile to allow of a considerable amount of stretching during the 
passage of the relatively large ova. 
The cuticle is reflected inwards at the margins of the genital orifice, 
and forms a continuous chitinous lining to the vagina, extending as far 
as the point of junction of the latter with the uterus. The reflected 
margin of both lips of the genital orifice is beset with short, stiff, curved 
hairs, which are particularly numerous on the anterior lip. The terminal 
portion of the vagirra is capable of being completely prolapsed through 
the genital orifice, a condition which normally appears during the 
extrusion of the ova. 
The genital orifice of the male (see PI. Ill, fig. 3, gen.ap.) occupies 
a corresponding position, but is considerably smaller than that of the 
female. It has the form of a strongly arched, crescentic slit, the convexity 
