BYRNES: CYCLOPS OF FRESH WATER. 



I. Introduction. 



The observations recorded in this Monograph have extended over 

 several years and have been made with special reference to the 

 variability of the Cyclops of fresh water. While in many instances 

 too few individuals of a species have been studied to permit of the 

 drawing of conclusions in regard to the tendencies of the species 

 to vary in any given direction, special care has been taken to record 

 such differences as have been observed between the Long Island 

 forms and those described and figured by earlier American 

 authors. 



The plates illustrate such forms as have been seen mainly in 

 the waters of the western section of Long Island. 



The figures have all been drawn to the same scale in order to 

 preserve the relative sizes of the various forms, and care has been 

 taken to reproduce accurately all such details as have been con- 

 sidered. Numerous experiments have been made in the rearing of 

 certain species to test the relationship of closely allied forms 

 and some few relationships have been clearly established through 

 this method which alone can be trusted to yield definite results 

 among forms as varied as are the fresh water Cyclops. 



This work has been carried on during two summers at Cold 

 Spring Harbor, Long Island, at the Laboratory of the Brooklyn 

 Institute of Arts and Sciences. My best thanks are due Professor 

 C. B. Davenport, Director of the Laboratory, for having placed at 

 my disposal the fullest facilities of the station, and for having read 

 the manuscript. 



Cyclops Ater (Plate I). 



Description of the Tzvo Forms. — Cyclops ater is one of the 

 more common forms of Cyclops found at Cold Spring Harbor, 

 Long Island. The adults present two distinct appearances ; the 

 distinctions are, however, limited to color, so far as my observa- 

 tions show. 



The two forms were collected in localities subjected to widely 

 different conditions. One form was found in pools of cold spring 

 water, completely covered by a dense growth of duck weed. It 



