THE NERVOUS SYSTEM OF THE LOBSTER. 321 



sur la partie correspondante du corps." " Chaque portion de la chaine 

 agit egalement d'une maniere directe sur le cote du corps qui lui 

 correspond. II n'y a pas d'entrecroisement dans le parcours des fibres 

 nerveuses." These results were obtained by stimulation with a needle 

 and by chemical stimulus. Electric stimulation was not employed. 



Although the normal passage of the nervous impulse is along the 

 same side of the nerve chain as that stimulated, the following experi- 

 ments show that when the normal path is interrupted by section, the 

 impulse can pass across the chain. 



(B) The nerve chain was cut completely across in front of the fourth 

 thoracic ganglion, and the interganglionic commissure on the right side 

 was cut just behind the same ganglion. On stimulating the stump of 

 the right commissure in front of and connected with the ganglion, the 

 fourth and fifth ambulatory limbs on the left side moved sharply ; this 

 shows that the impulse not being able to influence the limbs of the 

 same side, owing to the commissure being cut on that side, travelled 

 across the ganglion and acted on the limbs of the opposite side. 



(C) One of the thoracic ganglia was isolated by section of the cords 

 in front and behind. The large nerve to the limb of one side was cut 

 and its central end stimulated ; the limb of the opposite side moved 

 sharply, the impulse having passed directly across the ganglion. 



5. General Experiments on the Nervous System. 



(A) Stimulation of the cerebrum or supra-oesophageal ganglion 

 caused sharp movements of the antennae, thoracic appendages, and 

 abdomen. The animal crushed one claw within the other. The same 

 effects were observed when the oesophageal commissures were stimu- 

 lated, but the movements were even more violent. 



Yung obtained the same result by stimulating the cerebrum with a 

 needle and he points out that " le cerveau ou ganglion sur-oesophagien 

 est sensible sur toutes ses faces comme les autres ganglions, de la 

 chaine nerveuse, et contrairement a ce qui a lieu chez les insectes et 

 les vert£br£s " (p. 525). 



(B) Stimulation of the sub-ossophageal ganglion caused movements 

 of the masticatory appendages and maxillipedes ; also flapping of the 

 abdomen and movements of the thoracic appendages. 



(C) Stimulation of each thoracic ganglion caused movements, mainly 

 of the appendages which it supplied, but also movements of the appen- 

 dages behind, and flapping of the abdomen. 



w 



