American FisJicrics Society. 43 



and even if the task were possible, the continual changes would 

 render it fruitless. In the ocean attempts to do quantitative work 

 are rendered difficult by the great number of species of animals 

 present. In the fresh water the number -of species of minute 

 animals and plants present (excluding those that live in shore or 

 bottom) is only about eighty. When, now, it has announced that 

 a method has been found of counting, weighing and measuring all 

 the animals and plants occuring in a given volume of water in a 

 lake, or occurring in the whole lake, an immense stimulus was 

 at once afforded to the investigation of aquatic biology. The 

 animals and plants which live upon the shores or bottom of a 

 body of water form only a small part of all the organisms that it 

 contains. Far heavier and bulkier than the sum of these is the 

 sum of those minute forms that are found floating in the free 

 water removed from the influence of shore or bottom. These 

 forms are small and weak and are bufifeted about at the will of 

 waves and currents. Taken together they make up what we call 

 the plankton. The method which had now been devised was one 

 of measuring the organisms of the plankton, not those of shore 

 or bottom. It might seem at first sight that nothing could be 

 easier than to dip up a bucket of the water to be investigated, 

 filter it and weig'h and measure the animals. But it must be 

 remembered that water at dififerent depths might contain different 

 amounts of plankton, and hence it was necessary that the sample 

 of water taken should extend from the bottom to the surface, so 

 as to include water from all depths. The sample must bear the 

 same relation to the whole volume of water, that a disc punched 

 from the center of a sheet of metal bears to the whole sheet. No 

 simple method of actually removing such a sample of water from 

 a lake seems to be possible, but an exceedingly simple method 

 has been devised of removing the plankton from a sample column 

 of the water. This consists merely in drawing a fine net vertically 

 from the bottom to the surface. The contents of the net are 

 then removed and measured and weighed, and the individual 

 animals and plants which it contains are counted. It is necessarv 

 that the material used for the net should be so fine that it will 

 retain the minutest organisms, and such a material is found in 

 the finest bolting cloth used by millers. The net must further 

 be provided with a cup at the bottom to receive the minute 

 organisms w^iich are washed into it. Other precautions are 

 necessary both in taking the plankton and in its subsequent study, 

 but these need not be entered upon here. It is enough to know 

 that a properly constructed net drawn from the bottom to top 



