PHYSIOLOGY OB THE INVERTEBRATA. 331 



oesophageal ganglion. The latter nerves form the oesophageal 

 collar. The sub-ccsophageal ganglion supplies the somites, from 

 the fourth to the ninth, and their appendages, and gives off 

 also delicate nerves to the oosopliagus. The five anterior ab- 

 dominal ganglia supply the muscles and the appendages with 

 nerves ; while the sixth and last abdominal ganglion sends 

 nervous branches to the telson (tail). The sixth abdominal 

 ganglion also sends out two nerves, which unite into one 

 common trunk, and from which nerve-fibi'es are given off to 

 the intestine. The genital oi'gans are supplied with nerves 

 from the third, fourth, and fifth thoracic ganglia. 



" The size of the ganglia is in direct ratio with the 

 development of the segments and their appendages, to which 

 they belong " (Von Siebold). 



The physiology of the nerves of the Macrovra (under 

 stimulation) have been investigated by Drs. L. Fredericq and 

 G. Vandevelde.* They experimented upon the nerves of the 

 flexor muscles ot the chete of Homarus. The nerves of 

 Homarus when dissected out of the body very rapidly lose 

 their excitability, AV'hen a nerve is submitted to section the 

 excitability disappears progressively from the surface of the 

 section to the extremity of the periphery. Concerning 

 Homarus, Fredericq and Vandevelde state : " Ainsi, sur une 

 pince separee du corps de I'animal, il ai'rive un moment ou 

 I'excitation electrique du nerf pres de la surface de section ne 

 produit plus de contraction musculaire, alors que la meme 

 excitation appliquee sur un point plus rapproche du muscle 

 y provoque de violentes secousses." 



These experimenters have shown that the nerves of Homarui^ 

 present the same distribution of electric tensions, and the 

 same negative variation, as those of the frog {llana^. 



They have also ascertained the rate of transmission of 

 motor nervous influx in the nerve connected with the flexor 

 muscle of the dactylopodite. In these experiments they had 

 recourse to the graphic method employed by Hclmholtz. By 



* JJulletiiis (le VAcadimic lioija'e dt L'elfjI'juc, 2 serie, t. 47 [1S79]. 



