344 THE AMERICAN MONTHLY [Nov 



present in the sample can then be calculated very easily. 



This process has many things to be said in its favor, 

 and it is undoubtedly the best all-around method for the 

 study of the plankton. The apparatus required is simple, 

 inexpensive and not liable to get out of order. The pro- 

 cess is neither long nor difficult, and if care and cleanli- 

 ness are observed in the manipulation very accurate 

 results may be obtained. Ordinarily the quantity of 

 water operated upon is small, but there is no reason why 

 large filters may not be used. The writer has frequently 

 used a funnel having a neck one inch in diameter, filter- 

 ing from 1,000 to 10,000 c. c. This, when used with an 

 aspirator to hasten the filtration, has given excellent 

 satisfaction. The chief objection to the Sedgwick-Rafter 

 method is that delicate organisms are liable to be crushed 

 upon the sand, and this danger is naturally somewhat 

 greater when this aspirator is used. It is probably no 

 greater, however, than in Reighard's net. 



Recently a new apparatus has been devised for the 

 study of the microscopical organisms, known as the 

 planktonikrit. This is a modification of the centrifugal 

 machine and depends upon the fact that the specific grav- 

 ity of the organisms is different from that of water. It 

 has the advantage of avoiding, to a certain degree, the 

 crushing of the delicate infusoria, but it is somewhat 

 inaccurate in the case of some of the lighter organisms; 

 furthermore, it operates upon very small quantities of 

 water. 



In a complete study of the microscopical organisms, 

 such as might be undertaken on our great lakes, for 

 example, it would be advisable to use all three methods 

 adopting the Sedgwick-Rafter method for general quan- 

 titative work, but using the net and centrifugal appara- 

 tus for determining the rare and delicate organisms. 



As there are many lovers of the microscope who are 

 interested in studying aquatic life, and as there are many 



