86 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



59 a back view of that of a leech and of a crayfish. It 

 may be most simply described as consisting of a chain 

 of ganglia strung along the whole ventral aspect of the 

 body and below the alimentary canal, one to each joint, 

 connected by a single or double thread, and the most ante- 

 rior one — the (esophageal ganglion — being connected with 

 a large ganglion in the head, above the gullet — cephalic 

 ganglion — by two threads, one on each side of the gul- 



bs als ns 



Fig. 57. — Diagram of a crustacean ( I'ibilia) : is, blood system ; als, alimen- 

 tary system ; ns, nervous system. 



let, to form the (esophageal collar. It is a remarkable fact 

 that an oesophageal collar is found in nearly all inverte- 

 brates. 



Functions of the Several Ganglia. — The cephalic gan- 

 glion seems to preside over the higher senses, viz., the 

 eyes and the antenna. It is also the seat of conscious- 

 ness and volition and of whatever instinct or intelli- 

 gence the creature is possessed of, and, through its con- 

 nections with other ganglia, it dominates the whole body. 

 In a word, it corresponds in function to the cerebrum 



