PREFACE vil 
the following: to Professor C. M. Child, of the University of Chicago, 
for my first serious inspiration in natural history, and for my oppor- 
tunity to develop ecology; he has also rendered important assistance 
in connection with the preparation of this work, by giving information 
regarding animals about Chicago; his assistance with the worms and 
other lower invertebrates has been of particular importance; to Dr. H. C. 
Cowles, of the University of Chicago, for constant assistance with the 
plants and all matters relating to plant ecology. Various graduate 
students and assistants at the University of Chicago have also aided 
materially in the preservation of notes, specimens, and records. Mr. 
Beniah H. Dimmot, Dr. W. C. Allee, Mr. G. D. Allen, Mr. S. S. Visher, 
and Mr. M. M. Wells should be mentioned especially. Mabel Brown 
Shelford collected the data on the former occurrence of animals now 
extinct, and on other historical matters. 
The following have furnished identifications and important advice 
in connection with the various groups in which they are specialists: 
Dr. N. A. Harvey, Ypsilanti, Mich., Sponges. 
Dr. R. C. Osburn, Columbia University, Polyzoa. 
Dr. J. P. Moore, University of Pennsylvania, Leeches. 
Mr. F. C. Baker, Chicago Academy of Sciences, Mollusca. 
Dr. C. D. Marsh, U.S. Department of Agriculture, Copepods. 
Mr. Richard W. Sharpe, Brooklyn Institute, Ostracoda. 
Dr. Chauncey Juday, University of Wisconsin, Cladocera. 
Dr. E. A. Ortmann, Carnegie Museum, Crayfishes. 
Miss A. L. Weckel, Oak Park, Ill., Amphipods. 
Miss Harriet Richardson, U.S. National Museum, Isopods. 
Mr. O. F. Cook, U.S. Department of Agriculture, Myriopods. 
Dr. R. H. Wolcott, University of Nebraska, Water Mites. 
Mr. Nathan Banks, U.S. Department of Agriculture, Spiders. 
Mr. C. A. Hart, University of Illinois. All groups of insects. 
Dr. J. G. Needham, Cornell University, Aquatic insects. 
Dr. Cornelius Betten, Lake Forest University, Caddis-flies. 
Mr. W. J. Gerhard, Field Museum, Hemiptera and general entomology. 
Mr. A. B. Wolcott, Field Museum, Beetles. 
Prof. H. F. Wickham, University of Iowa, Beetles. 
Dr. Joseph Hancock, Chicago, Orthoptera. 
Mr. W. S. Blatchley, Indianapolis, Orthoptera. 
Dr. A. D. MacGillivray, University of Illinois, Sawflies and insect larvae. 
Dr. S. E. Meek and Mr. S. F. Hildebrand, Field Museum, Vertebrates. 
Mr. Alexander Kwiat, Chicago, Lepidoptera. 
Miss Clara Cunningham, South Bend, Tamarack Swamps. 
Dr. Frank Smith, University of Illinois, Annelids. 
