CLASSIFICATION 1(51 



The group Aphaneura may be thus defined : 



Oligochaeta tvith a ditellum confined to the ventral surface, with no male-ducts, 

 the female-ducts being replaced by a median pore, prostomium ciliated on the under 

 surface, ciliated pits on the head, reproduction by budding as well as by the sexual 

 process. 



As to the further division of the Microdrili, no one will dispute the justice of 

 placing in separate families (i) the Enchytraeidae, {%) the Moniligastridae, (3) the 

 Phreoryctidae. The remaining families of Naidomorpha, Tubificidae, and Lumbri- 

 culidae, I associate into one superfamily, giving my reasons for doing so on a 

 subsequent page ; this will form a fourth group, the Lumbriculides. 



The wide range of variation in structure exhibited by earthworms permits the 

 group to be broken up into families. 



This has been done by Peeeiee (3), Vejdovsky (24\ Benham (1), and Rosa (20), but there is 

 some difference in the classificatory systems of these authors. 



Peeeiee's classification ' depends primarily upon the relation of the male generative orifices to 

 the clitellum ; according to the position of the male generative orifices, earthworms are divided 

 into the following four groups : — 



(i) Anteclitellians : in which the male generative pores are in front 0/ the clitellum; 



(2) Intraclitellians : in which the male generative pores are within the clitellum ; 



(3) Postclitellians : in which the male generative pores are behind the clitellum ; 



(4) Aclitellians : in which there is no clitellum. 



The last division — that of the Aclitellians — cannot be defined as Peeeiee defined it, inasmuch as 

 BouENE (2) has discovered a clitellum in several Indian species of the genus Moniligaster, of which 

 genus alone the group consists. But the systematic position of Moniligaster has been already discussed. 



As Rosa (20) has pointed out, the classification of Peeeiee is artificial and must be abandoned 

 for three reasons: 



(i) It places in different groups genera which have close affinities in other respects. An 

 instance of this is Megascolex and Perichaeta ; the former genus is ' Intraulitellian ' the latter 

 ' PostcUtellian ' ; and yet Megascolex agrees with Perichaeta in such an important point as the 

 possession of numerous setae arranged in a ring, round the middle of each segment. 



(2) It separates species of the same genus. 



In the genus Acanthodrilus the following species are ' Postclitellian ' : ^A. obtusus, A. ungulatvs ; 

 the following are ' Intraclitellian ' : A. schlegelii, A. novae-zelandiae, A. dissimilis. 



(3) It separates even individuals of the same species. 



In some examples of Microscolex modestus, Rosa found the generative pores behind the clitellum, 

 in others within. 



Peeeiee himself remarked that EudHlus seemed to be a transitional form between the Intra- 

 and Postclitellian; the male sexual pores are within the clitellum, but the general organization of 

 the worm was rather that of the Postclitellian; and this principally for the reason that the male 

 reproductive ducts were furnished with prostate glands. In the present state of our knowledge, 



' This classification assumes that earthworms form a group 'Terricolae' equivalent to the 'Limicolae.' 



Y 



