Materials, Acknowledgments and Methods

At a late stage in the preparation of this manuscript a total of 5,457 specimens had been examined. For the most part these were conventional study-specimens; that is to say, they were stuffed skins with the skulls separate and each was accompanied by the customary data as to locality of capture, date of capture, name of collector, external measurements and sex recorded on the labels by the collectors. Skulls unaccompanied by skins, nevertheless, comprised a large share of the total and a small proportion was made up of skins unaccompanied by skulls, mounted specimens, skeletons, and entire animals preserved in liquid.

It was the recognition of this need for specimens from extensive areas from which no specimens previously had been collected that influenced me, approximately a year after the study was begun, to allot for it a long span of time. The procedure adopted, in general, was to study the weasels of one species from a given geographic area in so far as the material warranted, then lay this aside until additional critical material could be obtained, and finally, some months or a year later, complete the account. In this fashion the manuscript of the American weasels received my attention in each of the past twenty-five years (September, 1926 to date of publication). This is a confession of fact rather than a recommendation of procedure. This type of procedure unduly delays the diffusion of knowledge and for a variety of reasons justifiably annoys other students of the subject. Nevertheless, many gaps have been filled that otherwise would have remained open. Although specimens to solve several problems still remain to be collected and studied, it seems that a point of diminishing returns has now been reached, which, in fairness to all concerned, calls for publication of the results so far obtained.

For assistance in the entire undertaking, I am more indebted to Miss Annie M. Alexander than to any other one person; she provided the means by which specimens from critical areas were obtained, made it possible to examine the European collections, and assisted in other ways. The late Professor Joseph Grinnell and Mr. Charles D. Bunker, among others, gave truly valuable encouragement and assistance.

Collections containing weasels which were examined in the study here reported upon were as follows:

Acad. Nat. Sciences of Philadelphia

American Mus. Nat. History

Baylor University

Berlin Zoological Museum

Boston Society of Natural History

Brigham Young University

British Museum of Natural History

California Academy of Sciences

Carnegie Museum

Charleston Museum

Coe College

Collection of J. Arnold

Collection of Stanley C. Arthur

Collection of Rollin H. Baker

Collection of William Bebb

Collection of R. H. Coleman

Collection of Ian McTaggart-Cowan

Collection of Stuart Criddle

Collection of John Cushing

Collection of Walter W. Dalquest

Collection of William B. Davis

Collection of J. M. Edson

Collection of Ralph Ellis

Collection of John Fitzgerald, Jr.

Collection of Mr. Green

Collection of Ross Hardy

Collection of Donald V. Hemphill

Collection of L. M. Huey

Collection of R. W. Jackson

Collection of Stanley G. Jewett

Collection of E. J. Koestner

Collection of J. E. Law

Collection of A. H. Miller

Collection of Lloye H. Miller

Collection of R. D. Moore

Collection of J. A. Munro

Collection of O. J. Murie

Collection of Robert T. Orr

Collection of Arthur Peake

Collection of Kenneth Racey

Collection of William B. Richardson

Collection Rocky Mt. Spotted Fever Lab.

Collection of Victor B. Scheffer

Collection of William T. Shaw

Collection of O. P. Silliman

Collection of W. E. Snyder

Collection of Frank Stephens

Collection of T. C. Stephens

Collection of D. D. Stone

Collection of Myron H. Swenk

Collection of Joe and Dean Thiriot

Collection of John Tyler

Collection of Jack C vonBloeker

Collection of Alex Walker

Collection of Edward R. Warren

Colorado Museum of Natural History

Charles R. Conner Museum

Cornell University

Donald R. Dickey Collection

Field Museum of Natural History

Florida State Museum

Fresno State Junior College

Humboldt State Teachers College

Illinois Natural History Survey

Iowa State College

Iowa Wesleyan College

Kansas State Agric. College

Leland Stanford Junior University

Leningrad Academy of Science

Los Angeles Mus. Hist. Art and Sci.

Louisiana State University

Mt. Rainier Nat'l Park Collection

Museum of Comparative Zoölogy

Mus. Polonais d'Hist. Nat., Warsaw

Mus. Vert. Zoöl., Univ. California

Museum of Zoölogy, Univ. Michigan

National Museum of Canada

Naturhistoriska Ricksmuseum, Sweden

Neuchatel University Museum

New York State Museum

Ohio State Museum

Oklahoma Agric. and Mech. College

Ottawa University, Kansas

Paris Museum

Provincial Museum of British Columbia

Royal Ontario Museum of Zoölogy

San Diego Society of Natural History

State Hist. and Nat. Hist. Soc. Colo.

State Normal School, Cheney, Wash.

Texas Cooperative Research Collection

United States National Museum

University of Arkansas

Univ. California Mus. Palaeo.

University of Idaho

Univ. Kansas Mus. Nat. History

University of Minnesota

University of Notre Dame

University of Oklahoma

University of Oregon

University of South Dakota

University of Utah

Univ. Washington Museum of Zoölogy

University of Wisconsin

Univ. Zool. Mus., Copenhagen

The largest single collection is in the United States National Museum, where the specimens of the National Museum proper and the United States Biological Surveys Collection, together, provide essential materials including a large share of the holotypes. Specimens in all of the North American collections including Canada and México have been made available, by loan, and in 1937 materials were examined in the principal collections of northern and central Europe. After the materials in North American collections were assembled, special effort, with considerable success, was made in each of several winters, to obtain specimens from areas not previously represented in collections.

To the many persons who were in charge of the collections consulted, to those who at my request sought critical specimens, and to those who assisted in various stages of assembling data and in preparation of the manuscript, I am grateful indeed. Likewise, I am deeply appreciative of the grants-in-aid received from the Carnegie Institution of Washington, the University of California Chapter of Sigma Xi, the John Simon Guggenheim Memorial Foundation and the Kansas University Endowment Association. I am mindful also of an obligation to those who appropriated funds, by legislative action, for research use by The University of California and The University of Kansas.

For assistance with the illustrations I am indebted to the late Major Allan Brooks for Plate 1 , to Mrs. Mary Blos for figures 25-31, to Miss Ann Murray for figures 11-13, to Mr. W. C. Matthews for all the photographs, to Mrs. Freda L. Abernathy for figures 2-9, 18-22, 24, and for retouching all the photographs except the following which were retouched by Mrs. Virginia Unruh: figs. d of plates , , , , , , , ; figs. i of plates , , ; figs. h, j, k of plate ; figs. f and g of plates and ; and figs. c and d of plate . To Mrs. Unruh I am further indebted for figures , , and and for much terminal assistance with preparing most of the illustrations for the engraver.

The methods of study, after specimens were assembled, included first comparisons of specimens of like age and sex from each of several localities to ascertain the constant features by which full species were distinguishable, one from the other. For example, it was found that in every individual from Trout Lake, Washington, of the species here designated Mustela erminea, the postglenoidal length of the skull amounted to more than 47 per cent of the condylobasal length whereas it was less than 47 per cent in all individuals here designated as Mustela frenata, from the same locality. Testing of specimens from other localities by means of this and other selected characters permitted the outlining of the geographic ranges of the full "species-groups." By comparing specimens of other nominal species and by examining specimens from localities geographically intermediate between the nominal species, I found intergradation and therefore arranged the nominal species as subspecies of a single species. Intergradation here is understood to be the result of crossbreeding in nature between two kinds of animals in the area where the geographic ranges of the two kinds meet. Presence of intergradation between two kinds of weasels was basis for according them subspecific rank. Absence of intergradation in nature at every place where the geographic ranges of two kinds met or overlapped, and absence of intergradation by way of some other kind, or chain of kinds, was basis for according each of the two kinds full specific rank. By thus applying the test of intergradation, or lack of it, I found that there were four full species of weasels, of the subgenus Mustela, in all of the Americas.

Next, the specimens of one species were arranged in trays in a geographic sequence. The specimens from any one locality were segregated by sex and under one sex from one place were arranged from oldest to youngest, that is to say by age. The four series with the largest numbers of individuals of a given age were selected. Seventeen cranial measurements and three external measurements were recorded for each individual of each of these four series. For each measurement, the coefficient of variation, standard deviation and probable error were computed. The four samples subjected to such analysis were a series of adult males, one of adult females, one of subadult males and one of subadult females. Also, studies of each sex were made to ascertain seasonal changes in pelage. After data were obtained on ontogenetic (age) variation, secondary sexual variation, seasonal variation, and degree of individual variation by studying specimens in the manner described above, tests were made for subspecific (geographic) variation by comparing series of specimens of like sex, age and season, from different localities. For each one of several geographically variable features noted, a map was prepared for animals of each sex. When all the data thus obtained were codified, subspecific ranges were, in a sense automatically, obtained. On the resulting map showing geographic ranges of subspecies for a species, a type locality was accurately plotted for each name that had been applied to the species, and names then were applied in accordance with the international rules of zoölogical nomenclature.