TYPE CRUSTACEA. 



379 



on, a pair of ganglia occurring in each metaniere throughout 

 the body. Such a condition as this is found only in em- 

 bryonic stages, and even there not always perfectly. The 

 ganglia representing the preauteunulary metaniere fuse with 

 the cerebral, as do also the antenuulary, and in higher forms 

 the antennary ganglia, there being thus formed a complex 



FIG. 169. DIAGRAM OF NERVOUS 

 SYSTEM OF CRUSTACEAN. 

 ce = cerebral ganglion. 

 g ] = second 

 <7 2 = antennulary " 

 <7 3 = anteuuary " 

 mn rnandibular " 

 mx l , mx- = maxillary ganglia. 

 <K = oesophagus. 

 th l == first thoracic ganglion. 



tab 



FIG. 170. NERVOUS SYSTEM OP 



(A) AN ISOPOD, Asellus, AND 



(B) A BRACHYURAN DECAPOD, 



Maja (after MILNE-EDWABDS). 



cerebrum, which, in contrast to the simple cerebrum (arclii- 

 cerebrum) of the Annelida, may be known as a syncerebrum. 

 The remaining ganglia may remain perfectly separate, the 

 connectives joining the more anterior ones usually being 

 much shortened, or a greater or less number of them may 

 fuse. Thus in the Crayfish the ganglia of the three posterior 



