18 K. MITSUKUKI. 



phototaxis, and seems to disappear soon and on slight distur- 

 bances. 



5. While disliking deep water, Littorina exigua can not live on dry sur- 

 faces. It must have a car tain amount of moisture to crawl and 

 probably to feed. 



Note. This is the reason why the mollusc left dry at the 

 highest tide-level sleeps on, so to speak, unmindful of the 

 boiling heat of the midsummer sun, till the next spring- 

 tide comes round again in a fortnight and wets the region 

 about. 



G. Individuals of Littorina exigua do not probably wander about over 

 any large extent of space. 



Note. One individual which I marked, probably in August 

 or at the latest, earby in September, I found, had not stir- 

 red from the identical spot nearly four months later, on 

 Dec. 27, 1900. 



What is said here of Littorina exigua is probably true to a large 

 extent of the second species, L. sitchana, var. brevicula and of other 

 spBcies found elsewhere. 



In thinking over the facts thus brought out, it seems to me that the 

 facts under the second and fifth headings are probably the primary ones. 

 That is, the animal lived by preference on slightly moist surfaces of 

 rocks. Whenever the water became too deep for its comfort, it would 

 naturally try to escape toward shallower places more adapted to its life. 

 This they found, they could do by guiding themselves by their eyes toward 

 the quarter that appeared darkest to them. We know that this corresponds 

 with the direction of land, but it is not likely that the mollusc can have 

 any conception of the things presented to our mind by the words, land 

 and water. To the mollusc the dark quarter represents the comfortable 

 quarter, and nothing more. In course of ages, by the process of natural 

 selection, the mollusc would acquire the property of negative phototaxis 

 which has in actuality become so strong that even when the conditions 

 which originally made this property useful are artificially reversed, that 



