440 MR. W. E. COLLINGE OK ECTROPEAN SLUGS. \Maj 4, 



E. A. Pliilliijs, U. B. Eiu lib. ui'iie, II. i-'. acharii, E. W. Svvanton, 

 J. Taunton, A. T. AVilson, B. B. Woodward, G. W. Wood, and 

 Morris Toung. 



2. The Constancy of Anatomical Characters. 



During the last ten years nearly all the new species of Slugs 

 have been constituted upon diffei-ences in the form and position 

 of the generative organs, as may be readily seen by a reference to 

 the writings of Siraroth, 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 

 have elsewhere stated (8), for the separation of genera the aggre- 

 gate characters should be the basis for distinction ; but for specific 

 distinction the form and position of the generative organs is 

 imdoubtedly a reliable basis, provided that undue importance is 

 not attached to minute 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 Veronicella. A careful perusal of this paper 

 only proves, to my mind, that the results obtained are of little or 

 no value as regards the subject under discussion, for the authors 

 are ]iot certain whether they are dealing with variations in two, 

 three, or four species^ 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 under- 

 taken, it is surely necessarj'', 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 speci- 

 mens submitted to him as distinct species. 



