322 henry b. ward: 



in conjunction with numerous colaborers. Birge has devoted 

 himself singly to Lake Mendota and Marsh to Green Lake. 



Other investigators have turned their attention toward a 

 series of lakes or a given type of lake rather than toward 

 a single body of water. Thus Apsteiu (94) has achieved 

 valuable results from the study of Holstein lakes, Pero 

 has devoted himself to Swiss lakes in a single can- 

 ton and Hartwig to those of Brandenburg. But the 

 most s;riking instance of this specialization is Zschokke 

 whose investigations on elevated lakes have established so 

 clearly the biological features of such locations that subsequent 

 studies have added only details to the general picture he has 

 painted. The results of this author are summarized in a final 

 r i '.'.">) which presents further a comparison of the author's 

 work with that already achieved in other regions. This paper 

 Includes a careful study of two lake regions in the Alps, a 

 group of small sub-nival bodies of water in the Rhaeticon chain 

 and numerous lakes of \Vallis near St. Bernard. Both a littoral 

 and a limnetic fauna is present and in them most freshwater 

 groups an- represented, though in European nival and subnival 

 lake;- Helizoa, sponges, Bo&nzina, Isopoda and Decapoda are 

 wanting ami mollusks are- scantily represented. The bulk of 

 the Alpine freshwater fauna consists of resistent cosmopolitan 

 species which recur in part in lakes of high altitude elsewhere. 

 To these are added | 1 , here ami there rare forms from the 

 plains, (2) pure mountain forms often of northern character, 

 (3) abyssal inhabitants of sub-alpine lakes which find a suitable 

 environment on the shores of elevated Alpine lakes. The com- 

 position of the lacustrine fauna varies from place to place even 

 within a single mountain chain, but in general unfavorable en- 

 vironment increases with the altitude. The limit of suitable 

 environment, i. e. the upper limit of animal life, lies at dif- 

 ferent altitudes in different mountain ranges, but appears to be 

 higher in massive ranges than in neighboring chains of lesser 

 magnitude. The presence of certain forms adapted to the par- 

 ticular locality and the absence of other species imparts to the 

 scanty fauna of a mountain lake a decided individuality, often 



