Gee: Behavior of Leeches 219 



3. Feeding Reactions 



Upon the addition of a few drops of freshly macerated snail 

 juice to the water in a dish containing a number of Dina micro- 

 stoma these leeches are stimulated to greater activity. Rapid, 

 short-distance swimming reactions are given, the animals settling 

 quickly to the bottom of the dish, executing random feeling 

 movements, and, if successful, again swimming off or crawling 

 rapidly about in the dish. If while the animal is attached and 

 crawling a slight stimulus is applied by drawing a glass capillar}'' 

 rod up alongside of the anterior end, it reacts usually towards 

 it, applying the anterior sucker to the glass rod, and then quickly 

 withdrawing it. In many cases the anterior tip of the body is 

 coiled around the rod, and the anterior end applied to it, fol- 

 lowed by a recoil. Though momentary, it is yet a decided positive 

 reaction. This type of response is secured from contact stimulus 

 alone, as is discussed in a later portion of this work. However, 

 it is accentuated under the influence of diffusing food juices, as 

 well as by a starved condition of the leech. 



The food is located by "trial and error" movements, and is 

 often crawled over and under by the leeches without its presence 

 serving to check all of them. When the anterior sucker comes 

 in contact with the soft body of the snail there seems to be a 

 reinforcing stimulus to the contact response set up by the concen- 

 trated snail juice, and the animal holds on literally as well as 

 figuratively "for dear life." This constitutes the difference 

 between the response merely to contact under the influence of 

 diffuse snail juice, since there, due to the weakness of the food 

 juices, contact is not reinforced sufficiently to be followed up by 

 the feeding reaction. 



Whitman (1886) observed in one of the blood-leeches the 

 following: "A drop of fresh blood was allowed to flow from a 

 pipette over the dorsal surface of a leech while in a state of 

 repose. The leech kept up a gentle undulatory movement of 

 the body and gave no evidence of recognition. As soon, however, 

 as the blood flowed over the margin of the lip the leech became 

 aware of its presence." In Dina the application of macerated 

 snail juice was found to be effective only in producing greater 



