viii PREFACE. 



eral subscription, by letters, by articles in the journals, and by every means which the warmest 

 friendship and the most genuine interest in science could suggest. He was rewarded 

 beyond his utmost hope or mine, by the generous response of the public to whom he 

 appealed. We had fixed upon five hundred subscribers as the number necessary, to enter 

 upon the publication with safety ; and we had hoped that the list might perhaps be 

 increased to seven or eight hundred. At this moment it stands at twenty-five hundred : a 

 support such as was never before offered to any scientific man for purely scientific ends, 

 without any reference to government objects or direct practical aims, — although I believe 

 no scientific investigations, however abstruse, are without practical results. My generous 

 friend did not live to witness the completion of the first volume of the series, which 

 without his assistance could not have appeared, but he followed with the deepest interest 

 every step in its progress, to the day of his death ; — he did live, however, to hear the 

 echo which answered his appeal to the nation, in whose love of culture and liberality 

 towards all intellectual objects he had felt so much confidence. From all the principal 

 cities, and from towns and villages in the West, which a few years since did not exist; 

 from California, from every corner of the United States, — came not only names, but 

 proffers of assistance in the way of collections, and information respecting the distribution 

 and habits of animals, which have been of the utmost assistance in the progress of the 

 work. 



It has been my wish to make my part of the undertaking worthy of the interest so lib- 

 erally shown by the community ; and in this I have been greatly assisted by the liberal 

 views which the publishers have taken, from the beginning, with regard to its publication. 

 And now, in presenting this volume to the American public, I would take occasion to 

 repeat, — what has already been stated in a circular to my subscribers, — that the plan of 

 the work has been enlarged, in consequence of the liberality of the subscriptions, in a 

 manner which has delayed the publication for nearly a year, but which has, I believe, 

 made the book more valuable. I have thus been able to double, at the least, the num- 

 ber of figures upon most of the plates, and to include in the text, generalizations which 

 are the results of my whole scientific life ; so that this volume, — which, according to the 

 original plan, was designed to be one of special descriptive Zoology, — contains, in addition 

 to a description of the North American Tm-tles, a review of the classification of the whole 

 animal kingdom. I have also endeavored to make it a text-book of reference for the 

 student, in which he may find notices of all that has been accomplished in the various 

 departments of Natural History alluded to, and which, I trust, young American naturalists 

 will take not only as an indication of what has been done, but as an earnest of what 

 remains to be done, in the fields now open to our investigation. 



In consequence of these additions, the first volmne is more bulky than was intended, but 

 contains no plates ; while the second, in order to avoid mixing heterogeneous subjects, had 



