SEA-FISHERIES LABORATORY. 443 



Antennary nerve (a. 2 n.). One pair of small nerves, 

 which arise from the ventral side of the brain immediately 

 behind the tegumentary nerves. They are connected 

 with the fibres of the neuropiles of the second antenna. 

 Immediately on leaving the brain each passes beneath the 

 tegumentary nerve and enters the muscle chamber of the 

 second antenna. 



The commissures (Com.). One pair of rather large 

 nerves, which arise from the posterior side of the brain. 

 They pass posteriorly on each side of the oesophagus, and 

 are connected with the ventral nerve mass in the thorax. 

 At each side of the oesophagus there is a far oesophageal 

 ganglion (p. g.), and behind the oesophagus the two 

 commissures communicate by means of a transverse post- 

 oesophageal connective (n. po.). From the paroesophageal 

 ganglia arise the stomatogastric nerves, and immediately 

 behind the ganglion there is a small nerve (n. m.) 

 supplying the muscles of the mandibles. 



Ventral Nerve Mass. 



The ventral nerve mass (t. g.) is situated above the 

 sternal artery in the third and fourth thoracic somites. 

 It is partly supported by the median plate of the endo- 

 phragmal system. It contains nerve elements repre- 

 senting the post-oral cephalothoracic ganglia and the 

 abdominal ganglia. It is not possible to make out all 

 these ganglia from dissections, but they may be 

 distinguished in stained preparations and in sections. 

 Slightly behind the centre of this fused ganglionic mass 

 is a foramen (n. /.), through which passes the descending 

 artery. 



At its anterior end, where it is connected with the 

 commissure, the ventral nerve mass is narrower than in 

 its posterior portion. In this anterior portion it is 



