FRANDSEN. REACTIONS OF LIMAX MAXIMUS. 191 



questions will appear as these questions are considered. As the same 

 number of experiments were not made on each animal studied, I have, 

 for the sake of comparison, estimated in each case the geotaxis in per 

 cents. This percentage is obtained by dividing the number of positive 

 or negative responses by the total number of responses. The nearer the 

 geotaxis percentage approaches 100 the more precise has been the kind 

 of response. No fixed time was allowed to elapse between successive 

 tests, but in'each test the observation was made at an interval of from 30 

 to 60 seconds after covering the box. 



Operations and Results. — The first question investigated was whether 

 particular animals exhibited a decisive positive or negative geotaxis. A 

 number of tests were, therefore, made on each of several selected indi- 

 viduals. The results obtained were like those of Davenport and Perkins 

 ('97, p. 108) ; that is, certain animals showed a very marked positive geo- 

 taxis ; others, an equally decided negative tendency ; and a few, perhaps 

 one animal out of 12 or 15 where' 10 or more tests were made, were 

 apparently geotactically indifferent. The occasional irregularities in the 

 responses of individual animals were easily seen to be due to influences 

 other than pure gravity, such as jarrings of the plate, influence of contact 

 in putting the animal on the plate, and to the influence of light admitted 

 in lifting the cover of the box. Frequently, upon the raising of the 

 cloth to make an observation, the animal would retract its tentacles, as 

 if dazzled by the sudden inflow of light, and at the next observation 

 it would be seen to have altered its response. 



Naturally, this question next arose, Is the response the same on 

 different days? In Table IV. (p. 195) are given the results with a num- 

 ber of animals experimented on to test this point. These are numbers 

 2, 7, 8, 22-25, 27. Number 2 was positively geotactic on two days 

 and negative on another day. A similar variation is seen in the case 

 of slugs 7 and 22. In the case of all the rest, however, there is a very 

 marked constancy. The ninth (last) column in the table indicates the 

 condition of the animals at the time of experimentation. We see from 

 this that on the days of different response, the animals were in somewhat 

 unlike conditions, which may account for the irregularity of response. 

 The significance of this will be dealt with later. The important matter 

 here is, that the animals, when in the same condition and under the 

 same circumstances, have a fairly constant geotaxis from day to day. 

 One of the most marked cases is that of number 24. This animal was 

 experimented on at different times for a period of three weeks. During 

 this period, it was always active and in good condition, and, as the 



