366 



BIOLOGY. 



[BOOK vi. 



ganglion, and it usually furnishes nerves to certain organs of the 

 senses and regularly to the eyes. 



As a rule, the ganglions are constituted exclusively of cells, 

 and the cords exclusively of nervous fibres. 



FIG. 58. 



A, nervous system of a crab (Carcinus mcenas) ; gs, cerebral ganglion ; o, ocular nerve ; a, 

 nerve of the antennae ; c, oesophagian commissure ; transversal connection of this com- 

 missure ; gi, fusionated ventral chain. 



B, nervous system of a cirrhipod (Coronula diadema) seen in the ventral face : gs, c, gi, as 

 in A ; a, antennary nerves which distribute themselves over the mantle and the shell. 

 Between them is situated the ocular ganglion, in connection with the brain ; m, nerve of 

 the stomach ; s, visceral nerve which unites itself in a plexus s" with a second visceral 

 nerve *', coming from the anterior part of the- oesophagian ring. The abdominal ganglion 

 emits -forward the first cirrus, and rearward (nc) the other cirri. 



The body of the myriapods, and that of the grub or larva of 

 the insects, being formed of very numerous segments, the nervous 

 system of those animals is also very richly provided with gan- 

 glions. On the other hand a concentration, a coalescence, of 



