440 Proceedings of Royal Society of Edinburgh . [sess. 
The average length for males examined is 4*46 mm., whilst for 
females the figure is 3 7 3 mm. The measurements were taken 
from the tip of the body to the farther margin of the disc. In 
the males the posterior region is flattened upon the spine-bearing 
surface, and slightly keeled along the sides. The tip is usually 
curved upward; the genital opening is not quite terminal, and 
there is no marked cleft. In the female the body is expanded 
around the genital aperture, which is situated at the base of a 
well-marked cleft. This cleft is upon the lower or naked side of 
the body. 
As regards proportions of the sexes, it was noted that of 60 
specimens found, 15 proved males and 45 females. 
Body-iuall. 
There is a well-developed cuticle and sub-cuticle. The latter 
contains both longitudinal and circular fibrillse in which the spines 
are imbedded, and a hypodermis, in which are situated oval-shaped 
nuclei. The sub-cuticle in the region devoid of spines is thicker 
than in any other part of the body, and here, for the most part, 
are to be found the sub-cuticular lacunae. These consist of a 
system of very much branched canals, which interlace. They were 
not observed within the disc-like portion of the anterior region 
(fig. 4). The hypodermis shows a limiting membrane, against 
which is placed the musculature of the body-wall, arranged in 
closely set rows. The cells are nematoid in type ; in cross section 
they exhibit a U-shaped contractile portion, and a larger non-con- 
tractile part in which the nucleus lies. In most cases a single 
U-shaped part corresponds to a single cell, but cases were observed, 
usually occurring in groups, where as many as three or four ap- 
peared to possess a common non-contractile part, forming relatively 
a giant type of circular muscle cell. The longitudinal muscles are 
fewer, and here the contractile part encloses the non-contractile in 
a sheath-like manner. 
Proboscis Sheath and Nerve Ganglion. 
The proboscis or rostral sheath is double ; its retractor muscles 
at their terminations upon the body-wall divide up into a number 
