90 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
of a single ommatidium fusing on the proximal side to 
form a single nerve fibre (op. n.7.), which runs direct to 
the distal portion of the optic lobe. 
Sensory bristles.—On the flagellae of the large antennae 
there are a number of sensory bristles on each segment. 
These have been figured before by Némec (1895). Each 
bristle (PI. IV., fig. 3, s.b.) 1s enclosed by a sheath (sh), 
which is continuous with the rest of the cuticula (ctla.). The 
thick inner layer of chitin is pierced by a canal, the lumen 
of which is continuous with that of the bristle. From the 
bristle, by way of the canal, a number of delicate fibres 
(n. f.) run and communicate with a number of nerve fibres 
lying beneath the hypodermis (hyp.). These sensory 
bristles are probably the most important organs of sense 
which the animal possesses, as the antennae are con- 
tinually in use. Besides their undoubted tactile function, 
they may take the place of auditory organs. 
The inner of the two styles of the uropods, as 
described previously, are probably of a sensory nature. 
EXCRETORY SYSTEM. 
The excretory system may be studied in two ways—by 
feeding animals on food mixed with ammonium carminate 
or indigo-carmine, and by injecting aqueous solutions of 
these substances into the body cavity. The latter method 
is the most satisfactory, but should be supplemented by 
the first. The injections are made with a hypodermic 
syringe (or a pipette drawn out to a fine point). The 
animal is injected on the ventral side, at the base of one 
of the appendages, and may be killed from 5 to 48 hours 
after the injection and fixed in absolute alcohol or 
Flemming’s solution. 
The excretory organs of Isopods have been studied 
