134 Proceedings of the Royal Physical Society. 
doubly convex. Each disc presents the appearance of being made up of a 
number of segments. From the centre of each disc a short tube arises, the 
paired vasa deferentia, which unite to form the unpaired vas leading to the 
penis. Midway between the testes and the unpaired vas a short tube opens 
from the paired vasa and immediately branches into two long diverticula. 
Just below these short tubes the bulb-shaped sperm sacs lie. The unpaired 
vas deferens is formed by the junction of the paired vasa, and for about a 
third of its leneth is of the same diameter. It-then tapers, and, enclosed 
in chitin and muscle, enters the penis. The penis comprises three chitinous 
plates—the ring, the sheath, and the fork. The ring is a thin circular band 
Fre. 19.—Male Genital Forks (all to same scale). 
a. EH, ater, b. HH. palliatus, c. H. cunicularwus. 
of chitin encircling the sheath. It bears anteriorly a short projection, the 
anterior process. The sheath consists of a fine plate of chitin, the edges of 
which overlap and partly enclose the fleshy part of the penis. It extends 
anteriorly into two fine rods, the femora, which are attached to the ring and 
fork by muscle. Towards the base of the sheath two small plates arise from 
either side. The fork is a long chitinous rod diverging at its posterior end 
into two branches, a long and a short, not unlike the toe and heel of a boot, 
and terminating anteriorly in a flattened club (Fig. 19). 
These chitinous parts of the genitalia in the male serve as valuable 
characters for the identification of species. The fork is the most convenient 
of these characters. 
Female Reproductive Organs (Figs. 16, 17, 18).—These consist of the ovaries, 
the paired oviducts, the wnpaired oviduct or uterus, the receptaculum seminis, 
the bursa copulatrix, the vagina, and a pair of slime glands. The ovaries are two 
