318 C. F. MARSHALL. 



closing of the claw. This was repeated several times. This experi- 

 ment again shows that the large nerve contains both afferent and 

 efferent fibres : for we have seen above that the skin is sensitive to 

 external stimuli, and these passing up the large nerve must have 

 caused closing of the claw by reflex action through efferent fibres in 

 the same nerve, because the small nerve was cut. 



Experiment E. — In an active lobster the circum-oesophageal com- 

 missures were cut on both sides. This operation was performed by 

 making an aperture in the thorax and cutting with scissors where the 

 commissures were supposed to lie. That the commissures were really 

 cut was confirmed subsequently by i^ost mortem examination, a pre- 

 caution the necessity of which is evident. The connection between 

 the cerebrum and the rest of the nervous system was thus severed. 



The experiments A and B were then repeated. On cutting open the 

 limbs there ensued general movements much more marked than before, 

 the opposite limb being even brought over to the place of operation 

 manifestly for the purpose of removing the operating instruments. 



On stimulating the distal end of the small nerve the claw was 

 sharply opened, and on stimulating the central end of the same nerve 

 the claw was sharply closed by reflex action through the large nerve. 



In the opposite limb on stimulating the central end of the large 

 nerve the claw was sharply opened and the limb extended by reflex 

 action through the small nerve : and on stimulating the distal end of 

 the large nerve the claw was closed and the limb raised. 



All these actions were much more strongly marked and more regular 

 than in the case of the animals in which the connection with the cere- 

 brum was intact. This experiment shows that all the effects described 

 above are due to reflex action, and are more regular in action and 

 more strongly marked when the cerebrum is cut off from the rest of 

 the nervous system ; doubtless because inhibitory impulses which 

 might pass down from the cerebrum are stopped when the oesophageal 

 commissures are cut. This no doubt explains the faot that in some 

 of the animals experimented upon the effects described in A and B did 

 not all take place. 



Experiment F. — In another lobster the nerve chain was cut both in 

 front of and behind the second thoracic ganglion : the latter ganglion 

 which supplies the chelae was thus isolated (confirmed by post mortem 

 examination). The experiments A and B were performed on this animal 

 with the same results (excepting, of course, the general movements of 



