510 Mr. H. A. Baylis on 
about the thirtieth segment, and young mature segments 
begin at about the sixtieth. There may be about eight or 
nine gravid segments at the posterior end, but the number is 
never large. 
In a mature segment (fig. 7) there are about forty testes, 
occupying the posterior two-thirds of the segment, and ex- 
tending forwards on the aporal side of the ovary. The 
genital pores are irregularly alternating and situated near 
Fig. 7. 
Monopylidium stercorarium ; semi-diagrammatic drawing of a mature 
segment (from a whole preparation). 
C.S., cirrus-sac ; £., excretory canal; G.A., genital atrium; Ov., ovary ; 
R.S., receptaculum seminis; S., shell-gland; 7., testes; V., yolk- 
gland; V.D., vas deferens; Vj., vagina. 
the anterior corner of the segment. ‘There is a muscular 
atrium (fig. 7, G.A.) into which the male and female ducts 
open. ‘The cirrus-sac is small, measuring 0°15 x 0-037 mm. 
The vas deferens is long and much coiled, a large mass of its 
coils (fig. 7, V.D.) just between the cirrus-sac and the ovary 
functioning as a seminal vesicle. ‘The ovary consists of a 
larger and a smaller portion, the former being on the aporal 
side. Behind it is the yolk-gland, and between this and the 
SS a 
