DISTOMUM. 139 
The excretory system consists of a median duct which 
opens by a pore at the posterior end. It is connected with 
innumerable branches which form a fine net- 
work all over the body. Each branch eventually 
terminates in a blind swelling, in the centre of which there 
depends a fage/lum. The flickering motion of these flagella, 
doubtless causing currents towards the exterior, bas given 
the name of flame-cell excretory organs to the whole system. 
There are no known sense-organs, but the nervous 
system consists of a ring round the pharynx 
with two lateral ganglia and a small ventral 
ganglion. From the lateral ganglia are given off two 
ventro-lateral nerves which pass to the hind end of the 
body. 
Excretory. 
Nervous. 
Fig. 71.— STRUCTURE OF DISTOMUM. 
Ganglia. A, 
Nerve Ring. 
Right Lateral 4 
cee Left Lateral Nerve. 
ny As 
} \ ae 
Main Duct. . 2 
V \d 
Excretory Pore. 
A, Nervous System. B, Excretory System, 
The cavity of the body between the muscle layers and 
the alimentary and reproductive organs is almost entirely 
filled up with a mass of cells, arranged in 
a mesh-work, to which the name of parenchyma 
has been applied. Small cavities between these cells re- 
present the primitive vascular cavity or hemoccele. 
The reproductive organs are complex. D¢stomum is 
hermaphrodite. The female organs consist of a branched 
ovary on the right side of the animal, from 
which there passes an ovarian duct. Two 
large paired yolk-glands lie laterally and their viteldine ducts 
Vascular. 
Reproductive. 
