Manual of North American Diptera / by Samuel W. Williston.

  • Samuel Wendell Williston
Date:
1908
Catalogue details

Licence: In copyright

Credit: Manual of North American Diptera / by Samuel W. Williston. Source: Wellcome Collection.

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    in many cases. I can offer no better example of this dis- regard for phylogenetic and convergent evolution than is shown in the proposed scheme of classification of the Cecidomyidae on later pages. The structure and use of the organs of orientation,—the antennae and palpi especial- ly, the further comparative stud}^ of the ocelli and eyes, the reasons for the evolution of the wing venation in ap- parently different systems, the causes of the variations in the patterns of coloration, the meaning more fully of the different kinds of vestiture, etc., etc., all need much more attention than has been given them by the systematise and it is he who is best qualified to solve such problems. One of the first questions that a novice in classification asks is: What is a species, genus, family? The taxono- mist’s answer to the first of these queries is easy: A spe- cies is a form of life with all its fertile variants. A mas- tiff and a grayhound are not distinct species of dogs, because there exist all possible variations between the two types, though both have bred true to themselves for more than three thousand years. But a dog and a fox are distinct species because there exist no varieties con- necting the two. If no two specimens in a given form of fly have precisely the same relative lengths of the anten- nal joints, then the relative lengths of these organs is not a specific character in that form. If, however, all the specimens occurring in Massachusetts have a definite relative length for each joint while these in Kansas have another, the first impression is that they belong to dis- tinct species. If further discovery proves that, in cross- ing the country between Massachusetts and Kansas, the lengths gradually vary from one to the other, then we must consider the eastern and western specimens as mere- ly racial varieties of a single species. The systematist is never troubled as to what a species is, if he has all the material he wants.
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