Dee;p- Water Fauna of Lake Michigan. 101 



Also one species of parasite leech, found fastened to wliite- 

 fisli, and a small wMte Planaria. 



In conclusion, tlie occurrence of marine foi-ms {my sis and 

 iriglopsis) go far to prove tliat Lake Michigan was once salt ; 

 had direct communication with the ocean. As it gradually 

 became elevated above the sea it would naturally take many 

 years to expel the salt water, especially as its greater specific 

 gravity would cause it to sink and remain long in the lake 

 — time sufficient for the animals to become acclimated to the 

 changed condition of things. It is barely possible that salt 

 springs at the bottom of the lake may have materially retarded 

 the change ; and that even now there may be brackish water 

 in the greatest depths. This seems the more probable since 

 the salt-bearing strata occurs in Michigan. We made an effort 

 to solve the query, but owing to the imperfection of the appa- 

 ratus I am not certain that the negative was proved. 



H. 



