VERTICAL DISTRIBUTION OF THE LOWER PLANTS 

 AND ANIMALS IN THE INLAND LAKES. 



By PROF. E. A. BIRQE, of Wisconsin. 



Prof. Birge: I did not expect to be called upon first and 

 have not much to say. During the past three years I have been 

 engaged in studying the history both of the distribution through- 

 out the year and the vertical distribution of the small Crustacea 

 of the lake which immediately adjoins the University of Wis- 

 consin, Lake Mendota. This lake is about six miles in length 

 and from three to four miles in width, and, as you see, a rather 

 large sheet of water as inland lakes go. It is a lake of some 85 

 feet in greatest depth, the greater portion of the lake being over 

 50 feet in depth. At a distance of about a cjuarter ot a mile from 

 the shore we reach a depth of about 60 feet and from that point 

 on to the middle of the lake the increase in depth is quite slow, 

 so that the greater portion of the lake is a plain varying only 

 ten or 'fifteen feet from level. 



In studying the vertical distribution of these animals I em- 

 ployed a kind of a dredge so constructed that it could be lowered 

 to a givenTlepth, opened under the water, and then raised through 

 any desired distance and closed again when it had reached the 

 proper height. In that way it was possible to obtain the living 

 plants and animals between certain depths. It is opened at the 

 bottom, is then raised, say ten feet, is then closed and brought to 

 the top and the contents taken out. In that w^ay it is possible 

 to get the plants and animals of the lakes from each stratum. 



It is not my intention to go into the details of the distribu- 

 tion, but to call attention to one point only which seems to me 

 to have some practical bearing. In order to explain that, it is 

 necessary to speak of the -temperature of these lakes. As we all 

 know, the temperature of the bottom of our great lakes or inland 

 lakes is decidedly lower than the temperature at the surface. 

 While in Lake Mendota, for example, the temperature at the 

 surface during the summer is 75° or even 80° on the hottest 

 days, the temperature at the bottom is quite constant, somewhere 

 from 50 to 60 degrees, varying with the different seasons, at 

 a depth anywhere from 50 to 80 feet. The decline in temper- 

 ature from the surface to the bottom is by no means a regular 



