48 OKIGIN OF LIFE IN AMERICA 



biological evidence, though it Is usually argued that the ocean 

 crept inland through the St. Lawrence or Hudson Eiver 

 Valley. 



Fifty years have elapsed since Professor Loven * first drew 

 attention to the presence of several crustaceans, allied to 

 marine forms, in Swedish lakes, and endeavoured to prove that 

 the latter -must have been covered by the sea in recent geo- 

 logical times. One of these crustaceans is the fresh-water 

 shrimp Mysis relicta, closely related to the common Arctic 

 marine form Mysis oculata. Since the latter does not occur in 

 the Baltic, the theory that Mysis relicta is a recent immigrant 

 from that sea is untenable. It seems much more probable 

 that it gradually developed from its marine relative Mysis 

 oculata, when the Arctic Ocean covered the lowlands of 

 northern Eussia, Sweden and northern Germany. This view 

 is confirmed by the fact that Mysis relicta has now been dis- 

 covered, along with other marine organisms, in several lakes, 

 all of which are situated within the area covered by the north 

 European drift. I have also alluded to its occurrence in 

 Lough Neagh in Ireland.f 



Now it is of great interest that this small freso.-wa.ter 

 shrimp Mysis relicta, which is so closely related to a marine 

 species, should also occur abundantly in Lakes Superior and 

 Michigan. First discovered in the stomach of a Coregonus 

 taken in Lake Michigan by Dr. Hoy, it was subsequently met 

 with by Dr. Stimpson,J living in about fifty fathoms of water 

 in the same lake. It has since been noticed in Lake Superior 

 by Messrs. Smith and Verrill, but in no other of the Canadian 

 lakes. This is in so far significant, as neither of these two 

 lakes are supposed to have been invaded by the sea in Glacial 

 and post-Glacial times. All that geologists acknowledge is 

 that the sea crept up the Hudson Eiver and the St. Lawrence, 

 as far as the western end of Lake Ontario. The latter and 

 Lake Champlain had then a marine fauna, and it is there 

 that we should expect Mysis relicta to occnr. 



But besides this fresh-water shrimp, another small 



* Loven, S., " Tiber einige Crustaceen." 



t Scharff, E. F., "European Animals," p. 155. 



J Stimpson, A., " Fauna of Lake Michigan," p. 403. 



