xiii CLASSIFICATION MICRODRILI AND MEGADRILI 373 



but they are not at all well-defined genera, and indeed the generic 

 distinctions of the whole family Cryptodrilidae are not in a 

 satisfactory condition. 



Classification. The Oligochaeta do not shade into the Poly- 

 chaeta so imperceptibly as might be inferred from the current 

 schemes of classification. Apart from minor points, which are 

 not universally characteristic of the two groups, though never 

 found except in one or the other, the Oligochaeta are to be 

 defined by the complicated reproductive system ; although in a 

 few undoubted Polychaets there is a faint approach to this in the 

 specialisation of some of the nephridia as sperm -receptacles and 

 even as sperm-ducts. But nowhere among the Polychaeta are 

 there the diversified sperm-ducts and oviducts, spermathecae and 

 sperm-sacs, that are universal among the Oligochaeta. More- 

 over, no Polychaet has a clitellum, which is so distinctive of the 

 Oligochaeta, and of their near allies the Leeches. Dr. Eisig has 

 compared the glandular modification of the integument at the 

 mouths of the sperm-ducts in the Capitellidae to the beginnings 

 of a clitellum. This may be the case, but it is, in my opinion, 

 more comparable to the similar glandular spots at the male pores 

 in earthworms. The reproductive glands in the Oligochaeta 

 (save for a few apparently abnormal cases) are restricted to at 

 most two pairs of each, which occur in the same individual ; the 

 Polychaeta being dioecious. There is, in short, no form known 

 which cannot be definitely referred to either the Polychaeta or 

 the Oligochaeta, excepting perhaps Ctenodrilus, the anatomy of 

 whose reproductive organs is at present unknown. 



It is a difficult task to classify the different families of the 

 Oligochaeta ; and to enter into the historical aspect of the matter 

 would take too much space. I am myself disposed to divide them 

 first of all into two main groups, for which I use Dr. Benham's l 

 names of Microdrili and Megadrili. 



The Microdrili are, as a rule, small and aquatic in habit ; 

 they have short sperm-ducts which open on to the exterior in 

 the segment which immediately follows that which contains the 

 internal aperture ; the clitellum is only one cell thick ; the egg- 

 sacs are large ; the epoch of sexual maturity is at a fixed period. 

 This group, to my thinking, includes the Moniligastridae ; 

 although Professor Bourne has denied my statement with regard 



"An Attempt to classify Earthworms, " Quart. J. Micr. Sci. xxxi. 1890, p. 201. 



