H. S. Pratt 
235 
that of the cirrus and the genital sinus. Its lumen is bounded by a 
cuticula (Figs. 6 and 7, 8) which is a continuation of that of the genital 
sinus and similar to it in structure, containing the same cuticular 
bristles. These bristles appear more delicate, however, than those in 
the genital sinus or in the cirrus. Embedded in the cuticula are also 
large, specialized spines similar to those in the cirrus (12). They differ 
from those in the cirrus, however, in some details of their structure. 
The base is not bulbous as in the cirrus, but is more or less flattened 
(Fig. 9, 2) and the cylindrical rim (13) reaching to the inner surface of 
the cuticula is longer. The spine (12) which projects from the base 
through the rim is usually somewhat shorter than in the cirrus and 
does not show the beaded periphery which characterizes it. These 
spines are present in every part of the metraterm and occur with about 
the same frequency as in the cirrus. They are not quite so conspicuous, 
however, as they do not appear to have such thick walls. At any rate 
they do not take stains so vividly as do the spines in the cirrus. 
The character of the cuticula of the metraterm does not differ 
throughout its whole extent. The musculature is very delicate and 
consists of fibres which could not be separated into distinct layers. 
The testes (Figs. 1 and 2, 40) are a pair of oval organs about 0-3 mm. 
long and half as thick which are situated one behind the other in the 
hinder half of the body. The posterior testis is usually somewhat 
longer than the anterior. When the body is much contracted the 
two testes are pressed closely together (Fig. 2); when it is much 
extended, however, they may be separated by a distance equal to about 
a quarter of their length. The vasa deferentia (Figs. I and 3, 44) pass 
forward to the cirrus sac. 
The ovary (Figs. 1, 2 and 3, 28) is a spherical body 0-23 mm. in 
diameter which is situated directly in front of the anterior testis, often 
apparently somewhat at the left of the medial line. In a much con¬ 
tracted worm it may be closely pressed against the testis (Fig. 2, 28) 
and its shape changed to an oval. In worms whose body is fully 
extended it may be separated by 0-2 mm. from the testis. 
The oviduct (Fig. 10, 29) emerges from the antero-dorsal surface 
of the ovary slightly to the left of the medial line and passes dorso- 
ventrally a short distance to the median area of the worm where it is 
joined by the median yolk duct (23) and the Laurer’s canal (21). It 
then passes forwards and immediately expands to form the uterus. 
This structure is short and thick, lying between the ovary and the 
hinder end of the metraterm and the cirrus sac and bounded laterally 
