100 S. J. HOLMES 



Let us illustrate this view by the results of some experiments on 

 the crayfish. If a piece of meat is placed a short distance in front 

 of a crayfish, the first response is usually a slight twitching of the 

 outer ramus of the antennules ; this is followed by chewing move- 

 ments of the mouth parts and restless movements of the legs; 

 the small chelipeds are moved back and forth and grasping motions 

 are made by the small pincers as if in the endeavor to find some 

 object. These movements may be followed by walking, and ex- 

 ploring movements of the large chelipeds. The coordinated 

 movements of the antennules, mouth parts and legs may be regarded 

 as a complicated form of chain reflex. If now we apply a stim- 

 ulus to any of the organs concerned, it tends to set up the reflexes 

 in the rest. If a drop of meat juice be applied by means of a 

 capillary pipette to the tip of a small cheliped the first response is 

 usually a twitching movement in the chela followed by an ex- 

 ploring movement of the limb. This is followed by similar move- 

 ments of the other chelipeds and chewing movements of the mouth 

 parts, and these by the twitching of the outer ramus of the anten- 

 nules. If the stimulus be applied to the maxillipeds the chewing 

 movements of the mouth parts are followed by the movements 

 of the antennules and the legs. Any reflex element in this chain 

 of reflexes involved in food taking tends to set off all the others. 



I have trained crayfish, by feeding them by hand, to come 

 toward me to get meat. At first I would very slowly bring a piece 

 of meat held in a fine forceps near the antennules. After the 

 movements of the antennules and mouth parts the grasping move- 

 ments of the chelipeds would result in securing the meat. After 

 some trials I would not allow the meat to be pulled away from the 

 forceps until the cra} r fish struggled awhile to secure it ; at the same 

 time I moved my hand about so as to accustom the animal to my 

 movements. There is a struggle between the instinct to flee 

 from a large moving object and the instinct to secure a savory 

 morsel which has been seized. With careful management the 

 latter instinct may be made to predominate over the former and 

 gradually the fear of one's movements becomes much reduced. 

 The crayfish finally came to associate the approach of my hand 

 with being fed and would rear up and hold out its large chelae, 



