31 
is long. In Spher. Acanthozonis (pl. VII, fig. 5a and fig. 5b) they are reduced to rounded 
eminences without sete. 
A genital area is found in all species of these three genera, and it is in some cases 
much smaller, in others somewhat larger than the head. In its most developed form it is a 
more or less thickly chitinised plate, which is sometimes nearly circular (Spheronella 
curtipes, pl. X, fig. 2e), mostly considerably broader than it is long, and not unfrequently with 
a more or less concave anterior or posterior margin. In this plate we find the genital 
apertures more or less close to each other, so that the distance between them is nearly 
always shorter than the length of each; they are usually placed near the posterior margin, 
seldom in the middle or even nearer the anterior margin. Sometimes the central part of 
the plate or two rather lateral parts of it are thin-skinned (pl. II, fig. 3b), and in this last 
case the plate is really reduced to an oval ring with a median longitudinal band. In Spher. 
Munnopsidis (pl. X, fig.4c) the plate is more than twice as broad as it is long, and a large 
inner part of the same shape as the outline is more thin-skinned; the genital apertures are 
placed transversely and somewhat further from each other than the length of each. In other 
species the plate is reduced to about two thirds of a more or less oval, transverse ring, the 
posterior margin of which is close to the genital apertures, whereas the sides are further 
removed from them. A further reduction is noticed e.g. in Spher. frontalis (pl. VII, fig. 61), 
where the more conspicuous parts consist only of a chitinous arch behind and outside each 
genital aperture, the two arches yet being connected in the median line. In Spher. micro- 
cephala (pl. VIII, fig. 2f) the genital area is much longer than it is broad, and the chitinised 
part of it forms a semi-circle which opens towards the front, its two extremities running 
forward and forming two rather long, nearly parallel and partly dilated lists. The genital 
apertures are — as stated above — nearly always closer to each other than the length of 
each, besides they are curved and placed in an oblique direction, so that their convex sides 
turn towards each other, and their anterior ends are much closer together than the posterior 
ones; e.g. in Spher. microcephala, and especially in Spher. Munnopsidis, these apertures 
are turned so as to be almost or quite transverse; and in Spher. Munnopsidis the distance 
between them is greater. Each genital aperture is provided with two chitinous lists, the 
lips, of which the hindmost one is nearest to the median line and covers the front part of 
the other lip, when the genital aperture is closed. From the outer lip proceeds a strong 
muscle outward and obliquely forward, its proximal end being attached to the inner side of 
the plate or to the ring mentioned above. The contraction of this muscle pulls outward the 
outer lip, thus opening the genital aperture (pl. XI, fig.4d). For this purpose the skin close 
outside the outer lip is always thin (in many figures kept in a grey tint) though the sur- 
rounding parts may be a pretty hard chitinous plate. 
In front of each genital aperture, at a shorter or longer distance from it, though 
always within the genital area, is a very diminutive orifice which forms the entrance to 
an oval or somewhat elongate vesicle, the receptaculum seminis (pl. I, fig. 3a,r). These two 
