March, 1921] Macro-Fauna of Mirror Lake 139 



This survey was not a quantitative one. But usually all 

 animals of a kind were collected as far as practicable. Numbers 

 of individuals are noted for all species listed in the table. Actual 

 numbers alone may not signify much. If there are 10 crayfishes 

 and 10 midge larvae in a collection from one station, the real 

 interpretation of these equal numbers would be that the cray- 

 fishes were abundant and the midge larvae rather scarce. 

 Relative abundance of these and all forms in balanced natural 

 situations should be known and also environmental conditions 

 in the body of water in question. Consequently in the body of 

 the paper, use is made when possible, of the terms rare, few^ 

 many, common, abundant and sometimes other qualifying 

 words. There always exists the difficulty of varying interpre- 

 tation of these words, but this objection is outweighed by the 

 value of the terms used in a way which carries some proper 

 comparative significance for the various animal kinds and 

 groups. 



Groups of animals not covered in the work of this survey 

 are mentioned here and not further referred to : Protozoa, 

 (Stehle '20), Rotifera, Gastrotricha, Nematoda. 



Compound microscope and binocular could not be used in 

 the rather hurried work of separation and preservation, though 

 they were later used in such identification of groups as the 

 writer could do. Entomostraca could be detected and trans- 

 ferred without the lens. They are included in the survey, but 

 the list is necessarily very incomplete, as no tow net was used 

 and no real plankton survey made. Only those taken in the 

 collecting above described were available. Ostracoda were 

 omitted, for none were seen except some in jars containing 

 material from Mirror Lake that had been in the laboratory for 

 some time, and which hence undoubtedly represented a devel- 

 opment under certain favorable conditions not exactly dupli- 

 cated in the pond at the time. 



Among Vertebrata comparatively little collecting was done. 

 Fishes were obtained in two seinings, Sept. 27 and Oct. 4, 1919. 

 Some vertebrate records were merely based on notes of spec- 

 imens seen or on positive evidence of their presence. Amphibia 

 were collected in the spring of 1920. 



Among Invertebrata, several small groups, of which spec- 

 imens were expected, were not at all represented in the col- 

 lections, namely Bryozoa, and among Insecta, the Gyrinidae. 



Insecta, the largest single group, receive more emphasis 

 than any other group. 



