31 



is long. In Sphcer. Acanthosonis (pi. VII, fig. 5 a and fig. 5 b) they are reduced to rounded 

 eminences without setae. 



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 [Sphceronella 

 curtipes, pi. X, fig. 2 e), 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 (pi. II, fig. 3 b), and in this last 

 case the plate is really reduced to an oval ring with a median longitudinal band. In Sphcer. 

 Munnopsidis (pi. X, fig. 4 c) 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 Sphcer. frontalis (pi. VII, fig. 6i), 

 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 Sphcer. micro- 

 cephala (pi. 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 Sphcer. microcephala , and especially in Sphcer. Munnopsidis , these apertures 

 are turned so as to be almost or quite transverse; and in Sphcer. 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. Prom 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 (pi. XI, fig. 4 d). Fortius 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 rcceptactdum seminis (pi. I, fig. 3a, r). These two 



