MULTIPLICITY AND SIGNIFICANCE OF AQUATIC 



ORGANISMS 



Number and Variety 



The life of our waters is both varied and abundant. It differs 

 from the life of the land chiefly in that the most conspicuous and 

 largest types of both animals and plants are lacking, but the number 

 and variety of the smaller forms and of the microscopic species is 

 abundant beyond all ordinary conception. One has only to glance 

 over the pages of such a work as The Life of Inland Waters by 

 Professor James G. Needham of Cornell and his colleague, Mr. J. T. 

 Lloyd, to find a wealth of information and abundant illustrations 

 of this life. In it one may become familiar with the various types 

 of aquatic environment, the various aquatic organisms, both plant 

 and animal forms, and with their adjustment to conditions of aquatic 

 life. One finds that they are organized into definite aquatic 

 societies which depend upon different conditions for their existence, 

 and accordingly occur in different places. More intensive treatment 

 of some of the same factors is found in the appropriate chapters of 

 a book by Professor V. E. Shelford entitled Animal Communities 

 in Temperate America; and, finally, if there is need to emphasize 

 the abundance and variety of such organisms, evidence will be 

 obtained from a recent work entitled Fresh-Water Biology which 

 I have published with the cooperation of a series of specialists on 

 various groups. It may indicate the wealth of the forms found in 

 North American fresh water to say that over noo pages are re- 

 quired to present a summary of the topic and the 1547 illustrations 

 used do not show even all the important genera as only a few forms 

 are figured under fishes, insects and plants. Under natural con- 

 ditions, the aquatic species are varied and beautiful in form and 

 extraordinarily abundant in numbers. 



Relation to Purity of Water 



Observation of any individual water body with reference to the 

 character of the organisms in it and the abundance of these smaller 

 types of life yields readily incontrovertible evidence with reference 

 to the purity of its water. For the most part these minute organisms 

 are confined to a limited area or, if distributed more widely, are 



