64 -^rt 2.— T. Kabnraki : 



glacial age. In the post glacial age, which immediately succeeded 

 the Alpine Dann stage and the Scandinavian Litorina time, the 

 rising of temperature was so great that it rendered the water ab- 

 solutely unsuitable to the stenothermal animals, and made life 

 possible only in deep caverns or in the deepest parts of lakes, where 

 the daylight cannot penetrate and the temperature is very low. 

 Some characters of abyssal forms therefore reappeared here, and in 

 the course of generations the eyes must have altogether disap- 

 peared, according to the law of degeneration, and in consequence 

 of their disuse in darkness, this ])lindness acquired constancy and 

 l)ecame the distinctive character of the species. The great heat, 

 however, gradually diminished as time went on, again giving them 

 the opportunity to progress upon the surface of the water, but the 

 eyes did not reacquire sight. 



To such blind examples I am al:)ie to add one more which I 

 myself have met with. It is a case of ITicrostomum sp. , which 

 occurs fairly abundantly at Zeze in the marginal part of Lake Biwa. 

 Another is an interesting species belonging to the jNIacrostomidae. 

 This latter was discovered by Professor Tanabe of the Technical 

 College of Kyoto in the aquarium dish containing a certain fresh- 

 water weed (Cladophora santei'l't), which was cari'ied back by him- 

 self from Lake Akan in Hokkaido. 



Brehm has, turning his attention to Yokoyama's view, placed 

 on record that it would be interesting to know whether in Japan 

 there exist no species of Niphargus and Planaria wholly destitute 

 of eyes, as this may help us tow^ards the determination of Thiene- 

 mann's theory described above. If in this part of the world there 

 were formerly found nu glaciations, as contended by Yokoyama, 

 the discovery of such blind planarians as described al)ove would 

 justify us in ignoring Thiexemann's view. As Japan appears, 

 however, to have undergone climatic changes nearly parallel to 

 those found in Europe, it cannot at present be denied that the 

 blindness of freshwater organisms represents one of the characters 

 of the glacial relicts. The question, however, deserves further 

 investigation. 



