22 OLIGOCHAETA 



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

 Hplocardia comwunis, however, there are, exceptionally, three pairs ; in all the 

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

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

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

 licroscopical examination ; but such examination shows them to be invariably 

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

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

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

 hey are often accompanied by glands. 



Affinities of Acanthodrilidae. 



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

 T^as some years ago before the discovery of types like Neodrilus and 'Acantkodrilus' 

 pegazzinii ; Benham's new genus Plagiochaeta, to which Bourne's ' Perichaeta ' 

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

 haetidae even than JDeinodrilus ; with .regard to this latter genus I pointed out its 

 utermediate characters between Perichaeta and Acantkodrilus in regard to the setae 

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

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

 g. s.). In Plagiochaeta there is an agi-eement with the Acanthodrilidae in the 

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

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

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

 Ive pairs; the paired condition of numerous setae is unlike the condition of the 

 etae in the Perichaetidae, where a grouping into pairs is not known unless in 

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

 Plagiochaeta. 



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

 night seem to indicate an approach to the family Cryptodrilidae ; MichAELSEN (10) 

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

 Uryptodrilid genus Dichogaster and Benhamia rosea; practically the only difierence 

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

 sairs of spermiducal glands; Miohaelsen, however, has perhaps not sufficiently 

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

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



