2(i 



of a single ommatidiuni fusing on the proximal side to 

 form a single nerve fibre (op.n.f.), 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 Nemec (1895). Each 

 bristle (PI. IV., fig. 3, s.b.) is enclosed by a sheath (sA), 

 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 functio}i, 

 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 waj' s — by 

 feedincr 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 ajjpendages, and may be killed from 3 to 48 hours 

 after the injection and fixed in absolute alcohol or 

 Flemming's solution. 



The excretory organs of Isojxxls have been studied 



