FRANDSEN. — REACTIONS OF LIMAX MAXIMUS. 223 



ment?, it seems pretty clear that there is a difference in the sensitiveness 

 of the right and left sides. There is also some indication of a slightly 

 greater average tendency to move to the right. But a further study of 

 the undirected movements of slugs in the dark is needed. 



Studies have been made by several observers on the undirected move- 

 ments of a number of different animals, chiefly ants and other insects. 

 In all animals experimented on, there appears to be a tendency to travel 

 in loops or constantly widening spirals. Man, when he loses his way, 

 travels in a circle. Some interesting observations have been made by 

 George and Elizabeth Peckham ('98, pp. 211-219) on the sense of 

 direction in the solitary wasps. When the wasp starts out from its nest, 

 it flies quite around it and gradually circles farther and farther away in a 

 constantly enlarging spiral, sometimes recrossing its path a number of 

 times. The authors' observations show that this action is to enable the 

 wasp to familiarize itself with its surroundings, so that it can find its way 

 home when it so desires. The similar phenomenon observed in other 

 insects, such as ants, is, no doubt, for the same purpose. Davenport 

 ('97, pp. 278-279) in his experiments on Amoebae found that, when 

 their movement was undirected by any external stimulus, they tended to 

 travel in curious spiral loops. Pouchet ('72, pp. 227-228) made obser- 

 vations on the movement of larvae of Musca (Lucilia) caesar in the dark. 

 There is a striking contrast between the paths given by him of the un- 

 directed movements and those made in response to the stimulus of light. 

 The tendency to travel in a gradually widening spiral has also been 

 observed by the writer in young frog and toad larvae — before the develop- 

 ment of mouth and eyes — when they are dislodged from the support to 

 which they are clinging. 



Most of the following experiments on the slug were made in a room 

 about 12 feet square. The floor was sometimes covered with cardboard 

 or paper, but in other experiments was left bare. Heavy curtains were 

 hung in front of the windows and light shut out as completely as possible. 

 The experiments were conducted at night, and the temperature of the 

 room was nearly, if not quite, constant. A slug was put on the floor in 

 the centre of the room and left to itself for two or three hours, sometimes 

 longer. By means of the mucous secretion, which hardened into white, 

 shiny flakes, the exact path of the animal could, in most cases, be easily 

 followed. This path was roughly reproduced by pencil on paper. A num- 

 ber of these paths are given in Figures 3-22, much reduced from the 

 actual space covered. The series here given includes all the animals 

 experimented on, with the exception of three individuals which did not 



