TREFACE. xi 



a work tliat would exemplify (lie nature of fiie investiijatioiis I have been tracing during 

 the last ten years, and show what is likely to be the character of the whole scries. I 

 have aimed, therefon\ in preparing these two volumes, to combine them in such a manner 

 as that they should form a whole. The First Part contains an exposition of the general views 

 I have arrived at, thus far, in my studies of Natural History. The Second Part shows 

 how I have attempted to apjjly these results to the .special study of Zoology, taking the 

 order of 'restndinata as an example. I believe, that, in America, where Turtles are every- 

 where common and greatly diversified, a student could not make a better beginning than 

 by a careful jjernsal of this j)art of my work, specimens in hand, with constant reference 

 to the second ih;ipter of the First Part. The Third Part exemplifies the bearing of Embry- 

 ology upon these general questions, while it contains the fullest illustration of the embry- 

 onic growth of the Testudinata. 



As stated above, I liave received contributions from every part of the country, and upon 

 the mast diversified subjects, relating to my studies, which I shall mention in their proper 

 place in the course of the publication of my work, and give to all due credit for their 

 assistance. For the present, I must limit myself to returning my special thanks to those 

 who have materially contributed to the preparation of the first two volumes, now about 

 to be published together. 



Above all, I must mention the Smithsonian Institution, whose officers, in the true 

 spirit of its founder, have largely contributed to the advancement of my researches, by 

 forwarding to me for examination, not only all the specimens of Testudinata collected for 

 the museum of the Institution, l)ut also those brought to Washington by the naturalists 

 of the (lillrrent parties that have explored the western territories, or crossed the continent 

 with the view of determining the best route for the Pacific Railroad. These specimens 

 have enabled me to determine the geogi'aphical distribution of this order of Reptiles with 

 a degree of precision which I could not have attained without this assistance. Besides this. 

 Professor J. Henry, the liberal Secretary of the Institution, has caused special collections of 

 Turtles to be made for me in those parts of the country from which I had few or no 

 specimens, and Professor Baird has spared no i)ains to carry out these benevolent intentions. 

 I have also received from Professor Baird a number of interesting specimens, which he 

 himself collected during his extensive excursions. To these gentlemen, therefore, I am 

 indebted in the highest degree. Other public institutions have also atibrdcd me valuable 

 assistance. In l'hil;uielj>hia, I have been able to comi>are the specimens of the nmseum 

 of the Academy of Natural Sciences, which contains the originals of the great work of 

 Dr. Holhrook on the Ri'i)liles of North America. The Trustees of the University of Oxford, 

 in Mississippi, have intrusted to me, at the request of Dr. L. Harper, tlie Reptiles of the 

 State Survey for examination; and besides these, I have received many valuable specimens 

 froin that State, thnniijli Prof. B. L. A\'ailes. Prof. Alexander Winehell has also sent me 



