June, 1919] Fauna of Rock Bottom Ponds 429 



the more active individuals these numbers are not absolutely 

 accurate in all cases. They are a fairly close approximation, 

 however, and are given in the belief that they serve to present 

 a better idea of numbers than the terms "scarce," "common," 

 "abundant," "numerous" and "few" which are relative and 

 depend largely on the individual using them. For various 

 reasons it was not possible to carry out this method at all times. 

 When it had to be omitted numbers have either been indicated 

 by the more relative method or they have been left out entirely. 

 For determining the numerical quantity of plankton species, 

 five samples were taken out of the total quantity derived from 

 100 liters of water and a count was made from each sample 

 with the Sedgewick-Rafter cell. 



The apparatus and methods used in collecting do not 

 require extensive mention. A convenient field outfit for deter- 

 mining carbon dioxide was loaned by Prof. Foulk of Ohio State 

 University. To determine the transparency of the water a 

 porcelain lined top from an ordinary glass fruit jar was used. 

 A simple dredge and several small nets were constantly needed. 



In plankton collection tow nets were used when merely a 

 sample was desired. These nets were maintained at a given 

 level, whether at the surface or any number of feet below the 

 surface, by means of a float which consisted of a small, tightly 

 closed tin can. For quantitative plankton work a small hand 

 pump of the type frequently employed in spraying was used. 

 One method of operation was to pump water into a vessel of 

 known capacity and then empty this into a net which was sus- 

 pended in the pond. Another way was to pump directly into the 

 net suspended in a vessel filled with water. The water then 

 flowed from this into a vessel of known capacity. The first 

 method seemed to give more accurate results for, unless the 

 stream of water from the pump issued with very little force, 

 some plankton forms were driven through the net. Either of 

 these methods makes it possible to measure the exact amount of 

 water passing through the net and avoids the possible error 

 which may arise in the use of a plankton net or even of k 

 calibrated pump. 



For obtaining water from levels several feet below the sur- 

 face a garden hose was attached to the pump. White rings 

 were plainted on it at intervals of a foot to facilitate the deter- 

 mination of the depth at which the pumping was to be made. 



