508 Mr. H. A. Baylis on 
atrium towards the anterior border of the segment, and ends 
at, or even beyond, the middle line. The testes (fig. 4, 7’) 
number about twenty, and occupy the posterior half of the 
segment. here is a much-coiled vas deferens. The ovary 
consists of two groups of lobes, the larger group being on the 
aporal side. Between the two portions of the ovary there is 
a large rounded receptaculum seminis (fig. 4, .S.) ; close to 
Fig. 4. 
7 ‘ 
Monopylidium arcticum ; semi-diagrammatic drawing of a mature 
segment (from a whole preparation). : 
C.S., cirrus-sac ; G.A., genital atrium ; Ov., ovary; R.S., receptaculum 
seminis; S., shell-gland; 7., testes; V., yolk-gland; Vg., vagina. 
this is the shell-gland (fig. 4, S.), and behind both these the 
compact yolk-gland (fig. 4, V.). There are only a few ripe 
segments at the posterior end of the strobila. There is no 
definite uterus, the ova being embedded singly in the paren- 
chyme. The onchospheres are about 20 m in diameter. 
This form differs from J. cinguliferum (Krabbe) in a 
number of points, notably in its smaller number of testes, 
