518 OLIGOCHAETA 



In the genus Ocfochaetus the male pores are always outside of the ventral setae ; 

 this is not always the case with Acanthodrilus ; A. faldandicus is like Octochaetus 

 in this respect, but A. novae-zelavdiae has the male pores between the two setae of 

 the ventral pair ; the conspicuous groove which in this and in other species connects 

 the two atrial pores of each side of the body, and bears the sperm-duct-pore in its 

 course, passes exactly half way between the closely approximated setae of the ventral 

 pair (see woodcut, fig. 45). 



The clitelluTti is frequently saddle-shaped, that is, the thickened epidermis is 

 confined to the back and sides of the segments upon which the clitellum is developed, 

 and does not extend on to a ventral ai-ea bounded by the ventralmost setae of each 

 side : this state of affairs is, however, not always found upon the first few 

 segments of the clitellum ; it commonly commences with the segment just in front 

 of that bearing the reproductive pores. The clitell um is very variable in extent ; 

 in Beinodrihis benhami it is limited to three segments (xiv-xvi); in Trigaster 

 lankesteri segments xiii-xl constitute the clitellum ; the most usual segments upon 

 which it is developed are xiii-xvii. 



Dorsal pores are usually present ; but in a few species (e. g. A. georgianus) they 

 are entirely absent. The position of the first pore is naturally variable. 



In mature, and generally also in immature, Acanthodrilidae, the male genital pores 

 are extremely conspicuous ; these pores are nearly invariably — most exceptions that 

 have been described will probably prove in the long run not to be exceptions — upon 

 the seventeenth and nineteenth segments ; these apertures are those of the spermi- 

 ducal glands, and they are generally situated upon prominent papillae, corresponding 

 in position to the ventral setae ; on the eight^nth segment are the minute pores of 

 the sperm-ducts. Through the spermiducal gland-pores protrude the penial setae, when 

 these are present. A groove always connects the two pores of each side of the body. 

 Quite exceptionally, Neodrilus monocystis has only a single pair of spermiducal 

 gland-pores ; these are on the seventeenth segment ; a groove connects the pore of 

 each side with the sperm-duct pore on the eighteenth segment. 



The spermathecal pores in almost every species lie upon the boundary-line 

 between segments vii/viii, viii/ix, and con-espond in position to the pores on 

 xvii, xix ; in their neighbourhood there are occasionally papillae, but the presence of 

 such papillae is not at all characteristic of the family, as it is of the family Perichaetidae. 



The oviducal pores lie upon the fourteenth segment ; there are only one or two 

 species (e. g. Benhamia holavi) in which the female pore is single and median as it is 

 in the genus Ferichaeta (s. s.). 



The alimentai^y canal presents the same subdivisions as in other earthworms. 



