320 C. F. MAESHALL. 



the case of the posterior nerve which supplies the skin. On 

 stimulating the distal end of the latter nerve no effect was observed. 

 On stimulating the distal end of the anterior nerve which supplies 

 the abdominal appendage, the latter contracted. Hence the anterior 

 nerve would seem to be mixed, but the posterior nerve purely sensory. 



These results differ somewhat from those obtained by Yung. He 

 states that mechanical excitation of the two nerves produce the same 

 effect, each nerve being mixed (p. 487). 



With regard to the investigation of motor and sensory roots, Yung 

 does not appear to have experimented upon the nerves arising from 

 the thoracic ganglia. He says : — " Les racines des nerfs irradiant de 

 la chaine ventrale sont a la fois motrices et sensitives " (p. 525) ; but 

 this result was obtained only on the nerves arising from the abdominal 

 ganglia (p. 486). This result, as stated above, differs slightly from 

 the result I obtained from the abdominal nerves, one of which I found 

 to be mixed and the other purely sensory. Most of Yung's experi- 

 ments on the thoracic ganglia seem to have been performed with 

 a view to investigate the statement previously made by some 

 investigators that the superior and inferior surfaces of the ganglia 

 held a different function with regard to motion and sensation. 

 On page 525 we find : — " L'opinion classique, que la face inferieure 

 de la chaine est sensitive, tandis que la face superieure serait motrice, 

 est infirmee par nos experiences." 



4. Experiments on Decussation. 



(A) The oesophageal commissure of one side was cut and the an 

 terior end stimulated ; the antennae and autennules of the same side 

 moved sharply, those of the opposite side slightly. The same effect 

 took place when the other commissure was cut. Also the effects were 

 similar when the stimulation was performed on the other side. 



On stimulating the posterior end of each commissure, the thoracic 

 appendages moved mainly on the side stimulated, but slightly also on 

 the opposite side. The same effects were observed when the commis- 

 sures joining the separate ganglia were stimulated. 



These experiments show that there is no marked decussation of the 

 fibres as in vertebrates, for if it were so the effect would be more 

 marked on the opposite side of the body to that stimulated. 



Yung came to the following conclusions with regard to decussation 

 (pp. 525, 526) : " Chaque moitie droite et gauche du cerveau agit 



