128 DR. J. STEPHENSON ON THI': MORPHOLOGY, CLASSIFICATION, 



occurrence of two of these genem (Plutellus and Megascolides) in 

 JSTorth America is supposed to point to their having travelled 

 over the Angara continent. 



The other groups are less extensive ; they reinforce the above 

 conclusions, and permit the formulation of a fe\^■ more. 



(b) The Octochcetince. This subfamily, as stated in the pre- 

 vious article, originated from the common Notiodrilus ancestor 

 by a breaking up of the nephridial system ; the lines along 

 which evolution has advanced have also been mentioned. 



There is a form Hoioascolex in Madagascar in whicli the 

 breaking up of the nephridia has not proceeded far, meganephridia 

 coexisting with micionephridia. In OctochceUis the breaking up 

 is complete. Dinodrilus is derived from Octochcetus by a 

 multiplication of the setae to the number of six pniis instead of 

 four; the microscolecine reduction of the posterior male organs 

 without change in the number of setae leads to the genus 

 Euty2}hoeus. A continued increase of the numbei' of setae and 

 the consequent formation of complete chains was supposed to lead 

 to the evolution from Octochcettis of Hoplocluetella ; and in a 

 previous section I have given reasons for supposing that 

 Eudichogaster is also derived from Octochcetus by a reduplication 

 of the gizzard. 



Octochcetus is widely distributed in India, and occurs also in 

 ISTew Zealand, but not elsewhere — not in Australia. Dinodrilus 

 occurs in New Zealand only. Iloplochcetellcc was first found in 

 India, and species which were referred to it were subsequently 

 discovered in New Zealand, but these probably belong to a 

 different genus (20). Eatijphceus and Eudichogaster are purely 

 Indian genera. 



Here, then, we have relationships which differ from those 

 of the Megascolecinse ; they exclude Australia, and concern only 

 India and New Zealand. The conclusion is that at the time of 

 the dispersal of the Oetochfetinoe there was a connection between 

 India and New Zealand which did not extend to Australia ; 

 perhaps it passed entirely to the north, through the great 

 islands of the Malay Archipelago. The Octochaetinae do not 

 occur at present in the Malay Archipelago because they have 

 been unable to survive in competition with the dominant 

 Pheretima. 



(c) The TrigastrincB. This is a small subfamily — very small 

 as far as India is concerned. The essential character here is a 

 duplication or triplication of the gizzard. The parent genus 

 Diplocardia differs only in this respect from the Hotiodri'lus 

 ancestor of the whole family (Diplocardia and a closely similar 

 Senus Zapotecia have been regarded as constituting another 

 subfamily, the Diplocardiiuje). From Diplocardia is derived 

 Trigaster, in which the meganephridia have given place to 

 micronephridia ; it therefore has the original arrangement of 

 the male apparatus, lumbricine setae, micronephridia, and a 



