62 Art. 2.— T. Kaburaki : 



bottoms. It is also self-evident that the medium in which the 

 planarian lives has an influence on the distribution. Fl. (jonocephala 

 inhabits both stagnant and running water, while Poly, anrlculata 

 and especiallv PI. vivida are found in swiftly flowing streams: Poly, 

 auriculata on the other hand, seems to live only in streams with 

 sluggish currents. The chemical property of the water is also a 

 dominating factor in connexion with the distribution of planarians. 

 Though Poly, auriculata seems to abound in water containing a 

 considera])le quantity of organic substances, the planarian always 

 occurs in clear watei- and is not found in water containing mineral 

 substances to a certain degree. Poly, auriculata is chiefly found in 

 regions covered with dense forests of deciduous trees. It may be 

 stated that as all planarians are considerably negative in their 

 reaction to light, this is not a strong influence on their distribution. 

 Much has hitherto been written in favour of the view that 

 temperature seems to be a stronger influence than any otiier. I 

 am of the same opinion. As already mentioned, PI. vivida and 

 Poly. aî/?'ici//a^a always inhabit cold water in the northern mountain 

 districts, and are not found in the warmer legions such as Kiushu 

 and Shikoku. Of both the species, PI. vivida flourishes at a higher 

 altitude than Poly, auriculata, the former finding more security in 

 streams colder than those in which the latter occurs. Even in the 

 region in which they live together, PL vivida seems to be fitted 

 for life in the upper parts near the sources of streams, where the 

 water is colder than in the lower reaches. PL vivida, though ex- 

 tending much farther south than Poly, auricidata, is confined to 

 cold water either in caves at a low altitude or in higher mountain 

 districts. PL gonocephala which is very common throughout the 

 Empire inhabits streams of a higher temperature than the streams 

 in which PL vivida and Poly, auricidata exist. In the neigh- 

 bourhood of Yumoto is to be found this species in greater quantities, 

 but it is confined either to rivei"s or lakes, wliere the water was 

 decidedly lukewarm. Thus, it cannot be denied- that the tem- 

 perature appears to exercise a paramount influence upon the 

 distribution of planarians. 



, As mentioned above, it may be noted that the change of 



