522 OLIGOCHAETA 



The sperniathecae of the Acanthodrilidae are nearly always two pairs only; in 

 Diplocardia communis, however, there are, exceptionally, three pairs ; in all the 

 members of the family, except Kerria, the spermathecae have a diverticulum or 

 several diverticula ; it may happen that these appendices are so minute and so 

 concealed within the wall of the main pouch that they are invisible without 

 microscopical examination; but such examination shows them to be invariably 

 present ; these organs are invariably placed in the eighth and ninth segments. In 

 a few species, e.g. A. ungulatus and Benhamia beddardi, there are sacs of modified 

 setae, very similar to the penial setae, in the neighbourhood of the spermathecae ; 

 they are often accompanied by glands. 



Affinities of Acanthodrilidae. 



This family of earthworms is not so easily separable from other families as it 

 was some years ago before the discovery of types like Neodrilus and 'Acanthodrilus' 

 spegazzinii; BENHAM'S new genus Plagiochaeta, to which BOURNE'S ' Perichaeta' 

 stuarti may, perhaps, be referable, indicates a closer approach to the family Peri- 

 chaetidae even than Deinodrilus; with regard to this latter genus I pointed out its 

 intermediate characters between Perichaeta and Acanthodrilus in regard to the setae 

 and the clitellum ; the setae are twelve in number to each segment, and the clitellum 

 occupies the three segments found in nearly all the members of the genus Perichaeta 

 (s. s.). In Plagiochaeta there is an agreement with the Acanthodrilidae in the 

 existence of four spermiducal glands each provided with its bundle of penial setae, 

 in the presence of calciferous glands, and in the form of the spermathecae ; but the 

 setae are very numerous in each segment, being arranged in a series of about twenty- 

 five pau^s ; the paired condition of numerous setae is unlike the condition of the 

 setae in the Perichaetidac, where a grouping into pairs is not known unless in 

 Megascolex sylvestris of BUTTON, which may indeed be referable to the genus 

 Plagiochaeta. 



The disappearance, in Neodrilus, of the posterior pair of spermiducal glands 

 might seem to indicate an approach to the family Cryptodrilidae ; MICHAELSEN (10) 

 has compiled a very instructive table of the characters of two species of the 

 Cryptodrilid genus Dichogaster and Benhamia rosea; practically the only difference 

 between the Acanthodrilid and the Cryptodrilid is the presence in the latter of two 

 pairs of spermiducal glands; MICHAELSEN, however, has perhaps not sufficiently 

 emphasized the fact that in the Acanthodrilidae the sperm-ducts never open on to 

 the same segment as the glands ; whereas in Dichogaster and in all Cryptodrilids 



