78 SAKYO KANDA. 



on the disproportionately larger and heavier posterior region of 

 the animal" (3, p. 205). 



Judging from these statements, the center of gravity must lie 

 somewhere in the posterior region of the animal's body. In 

 other words, the posterior region is heavier than the anterior. 

 According to Frandsen, the negative geotropism of the animal 

 "on an inclined glass plate," however, is not due to the heaviness 

 of the posterior region, but to "the relative proportions of the 

 length of the anterior and the posterior regions of the animal's 

 body." In short, Frandsen's idea may be expressed thus: The 

 longer (and heavier?) posterior region being pulled by the con- 

 stant force of gravity, the slug becomes positive to it at the 

 minimal resistance in favor of the ratio above mentioned; on 

 the other hand, it becomes negative at the maximal in disfavor 

 of the ratio. In the latter sense, the "resistance theory," of 

 course, approaches the "mechanical theory." 



As pointed out before, this seems to be fairly supported by the 

 results obtained by the writer, which were given in Tables II., 

 III. and IV. This explanation is, however, focused to a limited 

 group of facts; because the snail becomes negative to gravity on 

 the nearly horizontal surface of a glass plate, where the minimal 

 resistance should be expected. This fact is opposed to Frandsen's 

 conclusion. Furthermore, as has already been shown, many 

 snails on the dry wooden plate at the angle of 90 of inclination 

 oriented themselves downward and crawled in that direction, 

 even though in so doing, they met a great mechanical difficulty 

 on account of the heavier posterior region. If the mechanical 

 theory of Frandsen is true, they were under the most favorable 

 conditions for crawling upward instead of downward. This was 

 not, however, the case. Was this because of the first factor of 

 Frandsen, that is, "the quantity and quality of the slime se- 

 creted" (3, p. 205). The second factor in question is by no means 

 separable from the first. Both go together. To make Frand- 

 sen's statement clearer, therefore, it may be expressed as follows: 

 'The relative proportions of the length of the anterior and the 

 posterior regions of the animal's body" "being the same, it is 

 this factor," that is, "the quantity and quality of the slime se- 

 creted," "which determines whether the head end will be directed 



