20 THE LIFE OF CRUSTACEA 



the outside through a small perforation on the 

 under-side of the first segment of the antenna. 



The chief part of the nervous system is the ventral 

 nerve-chain, which runs along the under-side of the 

 body. This is a long cord having at intervals a 

 series of knots or swellings, the ganglia or nerve- 

 centres, from which nerves are given off to the 

 appendages and to the organs of the body. In the 

 hinder part of the thorax and in the abdomen there 

 is a ganglion in each somite, but in front these 

 ganglia become crowded together and coalesced, so 

 that we find only a single large ganglion, correspond- 

 ing to the somites from that of the mandibles to 

 that of the third maxillipeds. Between the ganglia 

 the cord is really double, although for the greater 

 part of its length the two parts are more or less 

 completely fused into one. In front of the head and 

 above the gullet is a ganglion which sends nerves to 

 the eyes, antennules and antennae, and is known as 

 the hrain, although it is, perhaps, hardly so important 

 as that name would suggest. It is connected with 

 the ventral chain by two cords that pass on either 

 side of the gullet. 



The eyes, as already mentioned, are set on movable 

 stalks, so that they can be turned in any direction at 

 the will of the animal, and are of the type known as 

 " compound eyes." If the convex black area at the 

 end of the eye-stalk be examined with a strong lens, 

 it will be seen that the membrane which covers it is 



