Exploration of the Colorado River of the West and Its Tributaries Explored in 1869, 1870, 1871, and 1872, Under the Direction of the Secretary of the Smithsonian Institution.

Page 244, Exploration of the Colorado River

244 EXPLORATION OF THE CANONS OF THE COLORADO. ability to define species satisfactorily is a very good gauge of our ignorance of the whole truth. But naturalists practically work, for the most part, upon the surface of the subjects presented to their examination, not necessarily concerning themselves at all times with what lies hidden underneath. There are occasions to speculate and theorize, and there are other times when a naturalist may legitimately ignore underlying principles, and properly content himself with statement of certain observed facts. Working on this plane, as I am in the present instance, it is my business to render an exact account of what I find the case of Thomomys to be, without reference to abstract questions involved; and to sum the statement in such nomenclatural terms as I.may judge most suitable to express the relationships believed to subsist between the several differentiations which the genus has undergone. In describing the several forms of Thomomys, I waive the question of species; no harvest would be garnered if the laborers waited till they learned how the grain grew. In studying my specimens, I find that one of them differs from all the rest to such a degree that its characters are totally irreconcilable with those of any others. My description of it is merely an amplification of this statement. I give it a name, and call it a species, conventionally, simply in recognition of this fact, and for the usual purpose of readily indexing the items of information the specimen affords. I find, furthermore, that all the other specimens collectively present a varying sum of characters, according to difference in the emphasis of each one of these characters common to all; and that their interrelation or intergradation is so intimate and complete that no lines of precise distinction can be drawn ; but that, nevertheless, an average difference in three directions may be readily perceived and described intelligibly. It is an undoubted fact, furthermore, that these three differentiations are related in some way to certain geographical areas, for the simple reason that all the specimens of one style are produced in certain portions of the country, and all of the rest in certain other regions; and that the Thomomys existing on the confines of the several areas share each others' peculiarities. It is, once again, within the experience of those who have studied such subjects in their general bearings, that the aspects of the case presented by Thomomys tally exactly with those determined in a great many other cases.