2 FRESHWATER RHIZOPODS OF NORTH AMERICA. 



essentially aquatic, they occur wherever there is moisture. Commencing 

 from one's own doorstep, they may be found in almost every damp nook 

 and crevice, savanna and marsh, pool and ditch, pond and lake, sea and 

 ocean, and from the greatest depths of the latter to the snow-line of mount- 

 ains. By far the greater proportion are marine, and their tiny shells enter 

 abundantly into the composition of the ocean mud and abound in the sands 

 of every ocean shore. They appear to have been the first representatives 

 of animal life on earth; and if there is any truth in the theory of evolution, 

 they represent our own remotest ancestors. Having existed for ages, their 

 remains have largely contributed to the formation of the marine sediment- 

 ary rocks. 



The particular Rhizopods which form the subjects of the present work 

 are those usually designated as the 'Fresh-water Rhizopods', living mainly 

 in comparatively still fresh waters, in the mud of bogs, among algse and 

 mosses, and even on the ground in damp, shaded places. My investigations 

 were commenced four years ago, and have been continued during that time, 

 in intervals of leisure from teaching and ordinary business pursuits, until 

 last summer, when I began the preparation of my report for publication. 

 In the study of the Rhizopods, my attention has been more particularly 

 directed to the discovery and determination of the various forms occurring 

 in this country, rather than to the elaboration of details of structure, habits, 

 modes of development, and other matters pertaining to their history, 

 though these have not been entirely neglected. In the latter respects, my 

 researches fall short of those of some of the able naturalists of England and 

 Germany: — Wallich, Carter, and Archer of the former, and Hertwig and 

 Lesser, Greeff, Cienkowski, and Schulze of the latter country. 



The illustrations accompanying the work, done in chromo-lithography, 

 are not equal in execution to my desire, though they represent the charac- 

 teristic appearance of the subjects in all cases, I believe, sufficiently well to 

 enable the student to recognize these when found. The original drawings, 

 made by myself, I think may be fairly viewed as approximating accuracy, 

 at least so far as relates to the outlines, which have invariably been drawn 

 to a scale of measurements, so as to preserve the proportions of all parts. 

 Faults in perspective and other qualities are partially due to my own want 

 of ability as an artist, and partially to the difficulty of correctly interpret- 

 ing the views of objects as ordinarily seen through the microscope. Many 



