FRANDSEN. REACTIONS OF LIMAX MAXIMUS. 187 



the slug shall be directed up or down ? " was raised and considered. The 

 results showed that certain individuals appeared to have a fairly marked 

 positive geotaxis, for, when placed on an inclined glass plate, such 

 animals swung the head-pole of the axis toward the earth ; but others 

 showed as strongly marked a tendency to move away from the earth, and 

 a few seemed indifferent as to whether they went up or down. Their 

 experiments showed further that there was, apparently, no inherent 

 tendency in individual animals to move either to the right or to the left, 

 so that the difference in geotactic response could not be explained as due 

 to differences of an inherent tendency of this kind. The effect of a slight 

 initial impulse given to the head of the animal indicated that the thigcno- 

 tactic, or contact, stimulus imparted to the animal in handling might, to 

 some extent, modify its response to the stimulus of gravity. But 

 Davenport and Perkins did not reach any definite, satisfactory answer to 

 the main question. 



It was to test their observations by a larger number of experiments, 

 and, if confirmed, to explain them by further experimentation, that the 

 present investigation was undertaken. In the first place, I wished to 

 find out whether certain individuals, if put on an inclined glass plate, 

 always responded to the pull of gravity by directing the head end up and 

 moving away from the earth, and whether certain other individuals 

 always did the contrary. If this proved to be true, then it was my main 

 problem to seek the reason for it. Is the force which makes some slugs 

 go up, others down, and still others indifferent to the attraction of gravity, 

 a purely accidental one, — is it a physical force, or is it what we may call 

 a psychical peculiarity, which varies in different individuals and in the same 

 individual at different times ? As a preliminary to the main problem, 

 I first made a series of experiments on the animal's thigmotaxis, — its 

 response to contact- and pressure-stimuli. By virtue of its thigmotaxis, an 

 animal moves either toward or away from the agent which comes in 

 contact with it, just as its geotaxis is expressed in a movement toward or 

 away from the earth, in response to the attraction of gravity. 



I. Thigmotaxis. 



Material and Methods. — The animal used in all the following experi- 

 ments was Limax maximus, which is fairly abundant in the greenhouses 

 about Cambridge. Material was obtained from several different green- 

 houses and kept in a large closed tin box, the bottom of which was 

 covered with moss kept moist, so as to afford an environment as much like 

 the customary one as possible. Fresh cabbage leaves constituted the 



