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Show 440 MR. W. E. COLLINGE ON EUROPEAN SLUGS. [May 4 R. A. Phillips, 11. B. Raih.bjur.ue, R. F. Scharff, E. W. Swanton, J. Taunton, A. T. Wilson, B. B. Woodward, G. W . Wood, and Morris Young. 2. The Constancg of Anatomical Characters. During the last ten years nearly all the new species of Slugs have been constituted upon differences in the form and position of the generative organs, as may be readily seen by a reference to the writings of Simroth, Lessona, Pollonera, Godwin-Austen, and others. The external characters of such a group are exceedingly unreliable, for the colour, markings, &c. are liable to a wide range of variation in each individual species. Mr. Cockerell (3) has very decidedly questioned-strange as it may seem-the validity of anatomical characters for generic or specific distinction. Writing in 1892 (3. p. 4) he says :-" Here there is undoubtedly danger of error, since it is difficult to find out in many cases what is the stability of the apparent anatomical distinction. . . . Nothing should be more strongly insisted upon than the impossibility of applying the same tests of specific validity throughout series of genera; for characters that are generic in one place may not be specific in another." Mr. Cockerell is, I fear, dogmatizing upon a subject which he has not taken the trouble to actually work out; for, so far as I am aware, there is not a single valid genus of European Slugs in which good anatomical features cannot be set forth as characteristic of this or that particular genus. As I haA^e elsewhere stated (8), for the separation of genera the aggregate characters should be tbe basis for distinction ; but for specific distinction the form and position of the generative organs is undoubtedly a reliable basis, provided that undue importance is not attached to niinute variations due to age, season of the year, &c. More recently Messrs. Cockerell & Larkin (4) have attempted to substantiate the statement concerning the stability, or, as I prefer to term it, the constancy, of the form of certain parts of the generative organs in Veronlcella. A careful perusal of this paper only proves, to m y mind, that the results obtained are of little or no value as regards the subject under discussion, for the authors are not certain whether they are dealing with variations in two, three, or four species1. Some of the specimens, I am of opinion, were not full-grown, while in others the variations noted are of the most trifling character. Where such investigations are undertaken, it is surely necessary, if the results are to be of any value, to be quite certain of the species ; further, the number of specimens examined, and the proportion of variations found in each collection, if from more than one locality, should be stated. With a view to proving how little important variation occurs in the form of the terminal ducts of the generative organs, I have during the past four or five years carried out a series of investi- 1 In a footnote the authors state that Dr. Simroth considered some specimens submitted to him as distinct species. |