Benham. — Oligochaeta from Kermadec Islands. 



183 



Fig 



ately behind the pharynx, are so densely massed as to look like a gland ; 

 hut they occur less packed elsewhere.* 



Remarks. — There is still some doubt whether the genus Monopylephorus 

 of Levinsen is or is not identical with RMzodrihts of Smith (14), as 1 have 

 pointed out in my account of R. aucklandicus (1. p. 260). Although 

 Moore (13) retains the former title, I still 

 prefer to use the name Rhizodrilus, asso- 

 ciated as it is with the careful illustrated 

 articles by Smith and Goodrich. Seven 

 species of the genus have been described, 

 the description of one of which (R. 

 fluviatilis of Ferronniere) I have not 

 seen. 



The only species to which the pre- 

 sent one exhibits close resemblances 

 are R. pilosus Goodrich and R. (M.) 

 glaber Moore. 



With R. glaber the Kermadec worm 

 agrees, and therein differs from R. pilosus 

 in the following : (1) The arrangement 

 of the chaetae, their number and struc- 

 ture ; (2) in the arrangement of the 

 sperm-sacs, especially in that the pos- 

 terior sac does not enter the ovisac. 

 On the other hand, the form and struc- 

 ture of the spermiducal apparatus is 

 distinctly more like that in R. pilosus — 

 namely, in the proportion of the post- 

 prostatic region, in the relative size of 

 the transverse duct, and other details. 

 But in the present species the prostatic 

 region is more extensive, and the mus- 

 cular prostatic portion is shorter and takes a definitely transverse course, 

 with a distinct enlarged atrium and without the sigmoid undulations 

 shown in Goodrich's figure. 



It seems, therefore, to deserve recognition as a distinct species. At 

 the same time, one has to bear in mind that the two methods of study — 

 that by sections and that by examining and dissecting fresh specimens — 

 may account for some of the differences. For instance, while it is compara- 

 tivelv easy to dissect out in a fresh specimen the complete sperm apparatus,, 

 and thus determine accurately the proportions of the various regions, it 

 is next to impossible to determine these proportions by means of sections 

 unless one makes models of the sections and then reconstitutes the organ 

 in an enlarged condition — a matter for which I have not sufficient 

 time. 



Again, whereas Goodrich was working on the worm from a more or less 

 morphological point of view, and therefore failed perhaps to pay particular 

 attention to such things as the exact number of chaetae per bundle — as 



. 11. — R. kermadec en sis. Trans- 

 verse section (camera outline) 

 through the body in the region 

 of the male pore, a, dorsal 

 blood - vessel ; b, oesophagus ; 

 c, sperm -duct with pro- 

 state ; d, spermiducal chamber 

 (the dots in its wall indicate 

 the circular muscles) ; e, radial 

 muscles to body-wall. The 

 ventral blood-vessel is in black, 

 and the nerve-cord is dotted. 



* In these sections 1 find that the intestine, posterior to the sperm-sacs, is filled 

 with developing spermatozoa. I see no evidence of injury during sectionization, such 

 as the dragging of the cells by the razor, to account for their presence here ; but, as the 

 worm is bent in this region, it may be that they entered as a consequence of injury to- 

 the gut owing to a strong contraction on being killed. 



