The constant interest yon have shown in the progress of my Contributions to the Natural History of the United States, and the extensive assistance I have received from the Smithsonian Institution, induce me to address to you some remarks respecting the delay which has occurred in the publication of that work.

I feel it due to the public also, who have so generously sustained my undertaking, to say one word in explanation of this delay, and shall therefore take the liberty of publishing this letter after you have received it.

At the time that it was suggested to me to secure the means for publishing my investigations in this counti-y, by an appeal to the general culture and love of science in America, my highest hopes of success were limited to some hundreds of subscribers, and the plan of publication was arranged accordingly.

It soon became evident, however, that a much wider support would be offered to my work than had been anticipated ; and at this day I confess that my subscription list, with its twenty-five hundred names, looks to me like something almost fabulous.

The asstance I have received in the shape of specimens is quite as important.