OCR Text |
Show 1886.] LITTLE-KNOWN EARTHWORMS. 311 Normal Var. 1 „ 2 „ 3 „ 4 „ 5(2) ... ,. 6 .. 7 „ 8 „ 9 „ 10 „ 11 „ 12(2) ... „ 13(2) .. .. 14 „ 15 Spermathecae. 8 9 7,8 8,9 8.9 6,7 7, 8, 9,10 7, 8, 9 8, 9,10, 11 6,7,8 8, 9 (right); 9, 10 (left) 8, 9 (right); 9, 10 (left) 8,9 5 pores. 14 11 13,14 13,14 15,16 14,14 10 15,16 14,15 14 15,16 13,14 14 14, 15 15,17 15,16 d1 pores. 18 16 18 17 20 18 14, 15 18 18 17 19 16 18 18 21 IS Clitellum. 14 17 12-15 13-17 13-17 15-18 In considering a series of variations like the present, it is necessary in the first place to discriminate between what are really variations and what are specific characters. I have stated at the commencement of this paper m y belief that the anatomical differences between the individuals described here are variations, and not marks of specific difference. This opinion is based upon the following facts :-First, the exact correspondence in colour, size, and all anatomical characters, except those liable to variation, between the different individuals. It may, perhaps, be objected that it is begging the question to assume that it is precisely those characters which are liable to variation in this " species " that are unimportant as marks of specific difference ; especially when it is remembered that these differences mainly concern the genital system, which is well known to exhibit constant and regular variation, serving as a basis of classification. It is indeed perfectly true that this is the case ; but then the variations in the genital system are constantly accompanied by equally regular, though perhaps inconspicuous, variations in other characters ; so that a naturalist acquainted with this group could probably easily determine any species known to him by external characters only. It is not meant to imply by this statement that external characters are sufficient to decide the systematic position of an Earthworm, but merely to emphasize the fact that when, after dissection, the relations of internal structure to external form are known, the latter characters will serve as a guide to recognize the species. Secondly, the fact that the supposed variations are never represented by many specimens. Out of some 430 individuals I have recorded 15 variations, 12 of which are exhibited in as many specimens, while 3 are represented by two specimens apiece. The importance of this argument is in exact proportion to the number of specimens examined ; in the present instance it appears to m e to be fairly sound. Thirdly, Earthworms are known to vary somewhat in structure, |