572 Journal of Couiparatrce N^eurology an J Psychology. 



4. Extension movements of groping or searching, usually with 

 some uplift of tlie end and turning to and fro. Such movements 

 interrupt ordinary locomotion and are apt to be followed by a change 

 of direction. They show evidence of. increased sensitiveness in the 

 extended state, or what we may call the analogue of "attention." In 

 intense form they may simulate the appearance of pain reactions. 



5. In regard to the movements of the setae in locomotion there is 

 probability that the unusual arrangement of these stinictures in cir- 

 clets on each segment may be correlated with the peculiar forms of 

 movement described. They may assist not only in rolling but in 

 the very free movements of jumping which are characteristic of the 

 Perichjetidse. They are not, however, especially involved in the 

 problems here considered. The same may be said of other forms 

 of movement associated with food getting, etc. 



Metliods of StimuJatio7i. — Mechanical stimuli may be precisely 

 localized, but are difficult to graduate in intensity. Chemical stimuli 

 afford the readiest means of obtaining a graded series of intensities, 

 and may be fairly well localized. Acid solutions were used to evoke 

 the various grades of negative responses. Such stimuli are charac- 

 terized by the prolongation of their effects, with decreasing intensity 

 due largely to movements of the animal and extrusion of mucus. 

 Electrical stimulation has been tried to obtain the effects of a gi'adual 

 increase of intensity, by means of a rheonom. Some aspects of the 

 reactions to light have also been considered. 



Chemical Stimulatiox of the Anterior Exd. 



In the following account the results will be given of stimulation 

 with acid solutions (HCl) of different intensities. A unilateral 

 stimulus was applied with a fine brush within the first few segments. 

 The experiments were tried in dim light, with its effects as far as 

 possible equalized from different sides, the worms crawling on moist- 

 ened ground glass or filter paper. Perichseta gives a series of nega- 

 tive responses conditioned by the intensity of the stimukis coupled 

 with the physiological state of the animal. This series of reactions 

 vrill be described first, and then the frequency of their occurrence 



