222 University of California Piihlications in Zoology ["^o^. il 



in contact with the thin margin of the body that part nearest 

 the needle begins to retreat slowly before it. This behavior 

 shows a surprising keenness of tactile sensibility, the least touch 

 of the water with a needle point being felt at once. ' ' 



These experiments of Whitman were repeated on a couple 

 of specimens of Heniiclepsis occidentalis with the same striking 

 results recorded in his paper. Upon puncturing the surface film 

 the animal was observed to hug the bottom of the dish, remaining 

 quiet for a considerable length of time, often more than ten 

 minutes. Pricking the surface of the animal woiild produce 

 only a local contraction of the part stimulated without any gen- 

 eral movement of the body. The reaction is, as Whitman sug- 

 gests, very similar to that of the death feint in the higher inverte- 

 brates. Passing the hand over the dish will cause an active 

 Hemiclepsis to elevate the anterior end and exercise feeling move- 

 ments about in the water. The positive reaction to a shadow 

 seems to be absent in Dina, though a decided negative response 

 is secured to even very slight shadows cast over the dish. This 

 is particularly noticeable when the leeches are executing the 

 undulatory respiratory movements. 



The deceptive quiet of Dina microstoma is very much less 

 marked than in the Hemiclepsis above mentioned. Animals 

 placed in a circular glass dish 12 em. in diameter and containing 

 water to a depth of 2 em. were allowed to remain in a room with 

 rather dim, diffuse daylight without the slightest jar for four 

 hours and were in a slowly active condition. Then a glass rod 

 was applied to the surface film. In some cases the animal stopped 

 immediately and hugged the bottom of the dish for several 

 seconds. Again, little response was secured from some of the 

 individuals, these continuing their forward movements, entirely 

 disregarding the slight stimulus. An interval of fifteen to 

 eighteen hours of absolute quiet made the animal nnieh more 

 responsive to the slight stimulus, a much larger per cent showing 

 the deceptive quiet reaction. The duration of this is, however, 

 very much less than in Hemiclepsis. Contact stimulation of the 

 animal when in this condition of quiet, even of very slight 

 intensity, produces a marked negative reaction, a condition quite 

 different from that obtained in Hemiclepsis. 



