1^13] Gee: Behavior of Leeches 287 



non-adaptive, is indirectly of very decided advantage. The in- 

 creased activity upon which the intensified indifference is de- 

 pendent serves to bring the animal in contact with a wider field. 

 Its anterior end must necessarily come in touch with the surface 

 upon which it frequently comes to rest from swimming. Thus 

 with the increased number of attachments there would be an 

 increased likelihood of its successfully locating such food as 

 might be in its immediate environment. 



(&) Starved leeches. — Five leeches which had been starved 

 for forty-five days were subjected to a similar treatment to that 

 just described for the normal leeches. The accompanying table 

 (see table XIV) indicates the results secured. The predominance 

 of the negative response of the starved leeches in clean water is 

 to be attributed to the increased irritability of the starved indi- 

 viduals over that in the normal specimens. There is a striking 

 increase of the positive responses, and a considerable difference 

 in the number of indifferent responses under the influence of 

 the snail juice, both of which conditions serve to reduce the 

 number of negative responses in a striking degree. 



A comparison of the results secured from the starved indi- 

 viduals with those from the normal individuals affords a good 

 illustration of how the same external factor may affect two 

 organisms in different physiological states. It also serves to 

 show that the juices of the snail reinforce the tendencies toward 

 positive reaction to contact much more in the starved individual 

 than in the normal. It is scarcely necessary to emphasize the 

 adaptive nature of this difference in behavior. 



TABLE XIV 



Influence op Snail Juice Upon Reactions to Contact Stimuli in 

 Leeches Starved fob 45 Days. — Thirty Applications op Stimulus 



