7O SAKYO KANDA. 



of the slime secreted" makes it easier for the animals to crawl 

 downward or upward, as Frandsen thinks in the case of slugs 

 (3, p. 205). The question, however, arises: Why, then, did not 

 the snails crawl upward instead of downward on the the dry glass 

 and wooden plates? 



In this respect, Parker and Parshley offer a suggestive ex- 

 planation in the case of earthworms: "In the earthworm, the 

 response to dryness ... is apparently the selective extraction 

 of water from the peripheral protoplasm of the worm, a process 

 which is favored by capillarity of dry surfaces over which the 

 worm begins to creep and is probably dependent chiefly upon 

 evaporation from the surface of the worm itself. Under such 

 circumstances, the materials in the peripheral protoplasm of the 

 prostomium must become concentrated and probably initiates 

 stimulation by undergoing some such change as partial coagula- 

 tion" (15, p. 363). 



If so, the explanation must be looked for in physiological 

 conditions, that is, internal, rather than external mechanical 

 factors. As Parker and Parshley explain, the dryness of the 

 surface may cause the partial coagulation of the materials in 

 the peripheral protoplasm of the "foot" as well as of the anterior 

 geo-sensitive region of the snails, which may also result in surface- 

 tension changes and contraction of "muscle elements," and 

 cause the motion of displacement or coalescence of the fluid 

 materials in the protoplasm of the muscle-fibers and internal 

 cells (as Lillie thinks; 7, pp. 252-255), which possess different 

 specific gravities. Under such circumstances, we may assume a 

 disturbance in the peripheral as well as internal cells, especially 

 perhaps in the cells of the geo-sensitive region or the geotropic 

 organs, statocysts, which disturbance may be assumed to stimu- 

 late and cause the response of the animals. Whether the animal 

 will go up or down will depend on the other stimuli besides gravity, 

 such as character of surface and degree of dryness which accom- 

 pany the stimulation of gravity itself. This view quite agrees 

 w r ith Loeb's (9) and Lyon's (n or 6, pp. 20-21). 



