384 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XVIII. 



This represents eleven of the post-oral ganglia, those of the three 

 jaw somites and all eight thoracic somites united together with little 

 indication of their metameric segmentation beyond the fact that the 

 nerves radiate out from it to the eleven pair of appendages. There is 

 a large opening in the centre of these united ganglia through which 

 the sternal artery descends before it divides into its anterior and 

 posterior branches. 



In the abdomen we find a ganglion for each segment, the last sup- 

 plying the telson and giving a posterior visceral nerve to the hind-gut. 



In front, the stomach is supplied by an anterior viscerul nerve 

 which arises by three roots, — a median one from the posterior 

 surface of the brain, and two which arise, one on each side from the 

 para-cesophageal connectives and run transversely in to meet one 

 another and the median root and so form the visceral nerve. The 

 lateral roots of the nerve meeting in front of the gullet are sometimes 

 called the anterior commissure. Behind the gullet and in front of the 

 thoracic ganglicn is another transverse commissure, called the pos- 

 terior. 



In the Crabs, which are a higher race than Palinurus, we find a 



still further concentration 

 of the nerves, all seventeen 

 post-oral ganglia being 

 united into a large central 

 mass from which the 

 nerves radiate like the 

 spokes of a wheel. 



In the very young Pali- 

 nurus we find the nerve 

 cord double and the tho- 

 racic ganglia separate, and 

 it is only as development 

 proceeds that they amal- 

 gamate. Later when you 

 study the Mosquito you will 

 have a beautiful instance of 

 a similar coalescence of the 

 ganglia which you can 



*#. 



lo 



Wig, i.0.— Nervous svsteu ov a crab. 



Some crabs have no hole in the large gaugliou, the 

 sternal artery passlnar to one sUe. 



