THE ACTIONS OF BKAINLESS CRAYFISHES. Ill 



— a bit of metal, or wood, or paper, or one of the ani- 

 mal's own antennfE — is placed between the chelse of the 

 forceps, it is at once seized by them, and carried back- 

 wards ; the chelate ambulatory limbs are at the same 

 time advanced, the object seized is transferred to them, 

 and they at once tuck it between the external maxilli- 

 pedes, which, with the other jaws, begin vigorously to 

 masticate it. Sometimes the morsel is swallowed; 

 sometimes it passes out between the anterior jaws, as if 

 deglutition were difficult. It is very singular to observe 

 that, if the morsel which is being conveyed to the mouth 

 by one of the forceps is pulled back, the forceps and the 

 chelate ambulatory limbs of the other side are at once 

 brought forward to secure it. The movements of the 

 limbs are, in short, adjusted to meet the increased 

 resistance. 



All these phenomena cease at once, if the thoracic 

 ganglia are destroyed. It is in these, therefore, that the 

 simple stimulus set up by the contact of a body with, for 

 example, one of the forceps, is translated into all the sur- 

 prisingly complex and accurately co-ordinated movements, 

 which have been described. Thus the nervous system 

 of the crayfish may be regarded as a system of co-ordi- 

 nating mechanisms, each of which produces a certain 

 action, or set of actions, on the receipt of an appropriate 

 stimulus. 



When the crayfish comes into the world, it possesses 

 in its neuro-muscular apparatus certain innate poten- 



