1886.] 



LITTLE-KNOWN EARTHWORMS. 



311 



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 my 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 charac- 

 ters, 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 charac- 

 ters 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 me to be fairly 

 sound. 



Thirdly, Earthworms are known to vary somewhat in structure. 



