444 TRANSACTIONS LIVEBPOOL BIOLOGICAL SOCIETY. 



possible to make out, in suitable preparations, evidences 

 of six pairs of ganglia belonging to the last three cephalic 

 and the first three thoracic somites. Behind this region 

 five pairs of larger ganglia may be distinguished more 

 readily. From these arise the nerves supplying the five 

 pairs of pereiopods and the last five thoracic somites. 

 Between the last two ganglia is a median swelling, which 

 is composed of the six ganglia belonging to the abdominal 

 somites. 



The following nerves arise from the ventral nerve 

 mass : — 



First nerve (n. 1). One pair. Each arises close to 

 the connections between the commissure and the ventral 

 nerve mass. It contains fibres from the first three ganglia 

 of the nerve mass. It passes forwards parallel to the 

 commissure and divides into three branches, passing 

 to the mandible, first maxilla and second maxilla 

 respectively. 



Second nerve (n. 2). One pair. Each arises behind 

 the first nerve, and its fibres are connected with the cells 

 of the fourth ganglion of the nerve mass. It passes 

 forward and slightly outward, and supplies the various 

 parts of the first maxillipede. 



Nerves 3-9 (n. o-n. 9). These are all paired, and are 

 connected with the fifth and following ganglia of the 

 ventral mass. Each nerve supplies the appendage of its 

 own somite, and its course is very similar to that of the 

 second nerve. Nerves 5-9, however, are larger than the 

 others, and the posterior nerves pass outwards and back- 

 wards. 



Abdominal nerve (n. ah.). This is a median nerve, 

 which jDasses backward in the median line. It arises from 

 the fused abdominal ganglia at the posterior end of the 

 ventral nerve mass, and contains nerve fibres from all the 



