26 



ON THE LAMPREYS OF JAPAN AND SIBERIA. 



Sluggish creatures like the Lampreys can not naturally flourish in 

 rapid currents even when other conditions are favorable. Thus the 

 larger Lamprey which inhabits preferably the muddy bed of rivers, lakes, 

 ponds, and river-mouths ; and in the spawning season alone ascends rivers 

 to deposite eggs on the sandy bed of their tributaries, would not find 

 such conditions in the rapid streams of the Pacific slope. The poor 

 creatures could not be able to hold themselves. This, it seems to me, 

 sufficiently accounts for their absence from the river systems of that 

 side. 



On the other hand, the smaller Lamprey does not live in rivers, but 

 generally in small streamlets between the fields, in springs, or in small 

 canals near towns. The animal being thus independent of rivers their 

 habitation has been able to extend itself all over the main island wher- 

 ever other natural conditions allow them. 



There will be nothing to clash with the views put forward here, if 

 the larger Lamprey should be found hereafter, as is very likely, in 

 marshy regions of the Kwanto-Plain as well as in estuaries with the 

 muddy bed as the mouth of the Kiso Eiver and of the Kitakami Eiver, 

 although these localities belong to the Pacific side. On the contrary, 

 such a discovery could go a long way in proving the correctness of the 

 above hypothesis. 



Let us now turn to the examination of other islands : Shikoku, 

 Kyushu, and the Hokkaido, &c. 



Geologists tell us that the inland sea (the Setouchi-Umi) between 

 Shikoku, Kyüshü, and the main island was brought about lay faults 

 and constitutes a geological moat. The distribution of the Lampreys 

 affords the excellent evidence for this view. The two great southern 

 islands, Shikoku and Kyüshü, show, as regards the distribution of the 

 Lampreys, the same condition as the Pacific side of the main island ; on 

 these islands the smaller spacies alone is found ; they are to be regarded, 

 in this respect, as belonging to the Pacific slope. 



In the Hokkaido, only the slope facing the Japan Sea has been 

 explored ; in this part, the larger as well as smaller forms occur, just as 



