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THE AMERICAN NATURALIST [Vol. XLII 



crinoids there, which consequently are enabled to attain 

 very considerable dimensions. In the Kara and Barents 

 Seas there is no such supply of fresh water at hand, hence 

 the crinoids are small, but Spitzbergen, through its snow 

 fields, and the consequent freshening of the surface water 

 about it, allows the crinoids along its shores to reach a 

 larger size than those of the Barents and Kara Seas, 

 though they are not nearly so large as are those from 

 west Greenland. 



Over the Grand Banks the Gulf Stream brushes by, and 

 mixes more or less with, the cold northern current; this 

 is fatal to the delicate southern life it contains, which is 

 killed and precipitated to the crinoids below ; they, there- 

 fore, in spite of their living on the extreme southern limit 

 of the specific range, are as large as, or larger than, speci- 

 mens from Spitzbergen. 



The Kuro Shiwo, or Japanese current, sends off a 

 branch through the Korean Straits which washes the 

 eastern shore of the Japan Sea,' and in its northern part, 

 from the Straits of Tsugaru to the Straits of La Perouse 

 mingles with the very cold water from the Okhotsk Sea. 

 The mixing is very gradual and extends over a consider- 

 able territory, and over all this area the crinoids are of 

 gigantic size, bearing witness to their enormous food 

 supply. Now this colony of Heliometra glacicAis var. 

 maxima, a purely arctic species, replaced on the Pacific 

 side of Japan and the Kuril Islands by widely different 

 forms, and finding no close relatives nearer than the 

 Kara Sea, might be supposed in the course of the years 

 which have elapsed since the Okhotsk Sea was part of 

 the Arctic Ocean, to have become rather widely differen- 

 tiated from the parent stock, and to have gradually 

 reached a larger adult size from sonic other cause than 

 the question of food supply; fortunately, however, we are 

 able to make some observations bearing directly upon 

 this point. In this area, Heliometra is found where the 

 bottom temperature is very low, about freezing or less ; 

 but dovetailed into these cold areas are others where the 



