1904.] EARTHWORMS FROM NEW ZEALAND. 229 



Tliei'e are no penial ch^etaj. 



The ovaries are large and occupy the usual segment. 



There is a single pair of spermathecce in segment 9 ; each is a 

 subglobular sac (text-fig. 47) with a muscular duct, narrower than 

 the sac, which does not graduate into it but suddenly diminishes 

 in diameter. Two long tubular diverticula open, one on each side, 

 into the duct close to the body-wall. Each diverticulum, when 

 extended, is about twice the length of the sac. 



RemarJcs. — This genus, as I have remarked above, bears the 

 same sort of relation in regard to the prostates to Dinodrilus as 

 Neodrilus does to Maoi-idrihos ; but in JSfeodrilus, which Michael- 

 sen has termed a " microscolecine form," the number of testes has 

 also been reduced. Here, however, the reduction does not occur. 

 Moreover, Dinodrilus is micronephric instead of meganephric. 



We have in New Zealand a series of genera that illustrate the 

 evokition of Earthworms in a very remarkable manner. 



Starting with J^otiodrilus, which on general grounds is con- 

 sidered by Michaelsen as an ancient genus (and herein I agree 

 with him), we have a meganephric worm with 8 coupled chsetfe, 

 2 pail's of pi-ostates opening on segments 17 and 19, while the 

 sperm-ducts open independently on the intervening segment. 

 From this genus several lines of evolution start : — 



(a) Maoridrilus — which differs only in having alternately 



arranged nephridia, opening, that is to say, alternately in 

 relation to the dorsal and venti-al couples of chsetfe. 



(b) Neodrilits — in which the second pair of prostates, second 



pair of tubes, and spermathecse have disappeared, but male 

 pore still in the middle of segment 18. 



(c) Binodt'iloides — in which the number of chset^ is increased 



to 12 and widely separated, and in which the male pore is 

 close to the anterior margin of the 18th segment. 



(d) Rkododrilus — which still retains 8 clustei-s, but in which the 



male pore has moved forwards to the 17th segment and 

 opens close to the prostate pore. 



Starting again from JSfotiodrilus, we have Plagiochceta, which 

 differs from it chiefly in having a considerable number of chsetfe ; 

 and we readily see how this condition may have come about 

 through a Dinodrilus-Vtke form with 12 cheetfe. But in this 

 genus Plagiochceta, some, like P. sylvestris, have meganephridia, 

 others, like P. rossi, have micronephridia *. 



Once more reverting to our archaic genus, and imagining the 

 development of micronephridia, we reach Octochcstus, in which the 



* See Benliam ('02, a). The statement on pp. 287, 289, however, that P. rlcardi 

 and P. montana are siniilarh^ micronephric is erroneous. The nephridium is vei'y 

 small in proportion to the size of the worms, and the tubuli of the meganephridium 

 are in tufts, which, under an ordinary dissecting-lens, suggests a series of isolated 

 micronephridia ; but in P. rossi (laps. cal. rossii) the meganephridium has broken 

 up into micronephridia. I am jireparing an article on the nephridia of this and other 

 genera of New Zealand Earthworms, and for the present refrain from further detail. 



