n8 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



cesophageal ganglion will not interfere with the nor- 

 mal character of its eating movements. I give the 

 description in Bethe's words : " The animal devoid of 

 the supracesophageal ganglion is able to eat and 

 selects its food. It is true that pebbles, small 

 pieces of wood, etc., are seized by the forceps of the 

 front pairs of legs, but when brought near the mouth 

 they are rejected. A piece of meat, however, is 

 always taken into the mouth and masticated. The 

 swallowing is difficult, just as in the case of Carcinus. 

 The piece often remains for a long time between the 

 maxillipedes without being swallowed, and at last falls 

 to the ground. Pieces of paper that have been satu- 

 rated with meat-juice are treated in the same way. 

 Stones that have been covered with meat-juice are 

 also brought to the mouth, but no attempt is made to 

 masticate them. They are usually dropped as soon 

 as they come in contact with the maxillipedes." Thus 

 we see that the nature of the stimulus determines the 

 results just as in the case of Actinians. The brain of 

 the crayfish has nothing to do with these reactions. 

 The central nervous system is in this case to be con- 

 sidered only as an organ for the conduction of stimuli, 

 a function that could just as well be performed by plant 

 protoplasm or muscle-tissue as by nerve-protoplasm. 

 In the crayfish, the original segmental arrangement 

 of the nervous elements is so well preserved that re- 

 moval of the brain does not interrupt the proto- 

 plasmic nervous connection between the surface of the 

 mouth and the muscles of the thoracic appendages. 



