FRANDSEN. — REACTIONS OF LIMAX MAXIMUS. 205 



would seem that fear, by impelling the animal to escape from captivity, 

 may alter its geotatic response. Such freshly captured slugs, moreover, 

 which seem unusually restless and excited, respond more capriciously 

 to the stimulation of light, as some later experiments will show. 



Summary of Part II. 



The results of the foregoing experiments warrant the following con- 

 clusions : — 



1. On an inclined glass plate, all slugs give a geotactic response. 



2. Certain slugs give a decided positive, others a markedly negative 

 geotactic response; a few are somewhat indifferent. 



3. The geotaxis of animals kept in confinement does not vary much 

 on different days, nor at different times on the same day. 



4. The occasional vagaries in the responses of individual animals are 

 to some extent due to thigmotactic and phototactic influences. 



5. The different geotactic response, on a glass plate, of different indi- 

 viduals is due mainly to two factors : (a) The quantity and quality of the 

 slime secreted, which is a very important factor ; (b) the relative pro- 

 portions of the length of the anterior and the posterior regions of the 

 animal's body. All the conditions being the same, it is this factor 

 which " determines whether the head end will be directed up or down." 



6. If the ratio of length of anterior to posterior region of body is 2:3, 

 or more, and the mucus is of good quality and sufficient quantity, the 

 slug will be positively geotactic. 



7. If the ratio is 3 : 5, or less, the animal will usually migrate upward, 

 and the nearer the ratio approaches 1 : 2 the more apt is the slug to 

 respond negatively. 



8. In a small number of individuals, in which the ratio lies between 

 2 : 3 and 3 : 5, the response will depend largely on the condition of the 

 mucus and cooperation of other factors. 



9. All slugs have a natural tendency to move towards the earth. 

 This tendency is masked in the animals which are negatively geotactic 

 on a glass plate by the greater pull of gravity on the disproportionately 

 larger and heavier posterior region of the animal. 



10. The general downward tendency may vary normally at different 

 times of the day, owing to the animal's habit of remaining in concealment 

 in the daytime and feeding at night. 



