1 290 



BULLETIN OF THE BUREAU OF FISHERIES. 



underlying resemblances of that cycle as found in different lakes and also some 

 small part of the infinite variation in its details. These diagrams from late 

 summer represent the culminating point of an annually recurrent series of defi- 



nite changes through 

 which the lakes pass with 

 the season as certainly as 

 the season returns. These 

 changes result from the 

 interrelation of the living 

 beings of the lake with an 

 environment strictly lim- 

 ited in its space and con- 

 taining only definite 

 amounts of food and of 

 oxygen, to which only 

 small additions can be 

 made from the outside. 

 The story of these changes 

 is legible to him who will 

 closely follow it. Its de- 

 tails differ, indeed, in each 

 lake from those found in a neighboring lake, but on the whole it always follows 

 along certain great lines and shows that lakes can be grouped into classes 

 according to its major vari- 

 ants. Only a little of this 



0" 

 I 



story is now known, and 

 many years of detailed 

 work will be needed be- 

 fore even its larger facts 

 are fully ascertained and 

 justly interpreted. But 

 from the few diagrams 

 which I have given one 

 may see that lakes present 

 to the student a vital 

 story, as definite, as vari- 

 able, and as complex as 

 is that of a living organ- 



C 



.4 2 



T 34 36 



2 4 6 8 10 12 14 16 18 20 22 ZA 26. 2S 30 



C T 



Fig. 18. — Otter Lake, .\ugust 4, 1908. 



Cb 



ism; a story to be followed by means like those needed to work out biological 

 life histories, and one whose interest is such as to claim far more attention 

 from science than it has received. 



