ON TWO NEW GENERA OF AQUATIC OLIGOCHvETA. 291 



muscular tunic of atrium ; sperm duct furnished with a long convoluted diverticulum ; 

 oviducts opening on to intersegmental groove XII/XIII ; alimentary tract ciliated 

 throughout the entire length with the exception of the buccal cavity. 



Genus Phreodrilus, nov. gen. 



A single pair of very elongated and coiled spermathecse, opening on to exterior in 

 front of dorsal setse of segment XIII. Septal glands present, connected with pharynx. 

 Nephriclia wanting in anterior segments. No special sperm sacs or egg sacs. (?) 



Phreodrilus subterraneus, n.sp. 



Long, slender worm about 2 inches long ; chloragogen cells upon oesophagus com- 

 mence towards end of segment VI. Habitat, New Zealand. 



The above definitions must naturally be considered as very temporary ; they will no 

 doubt require revision in the event of the discovery of an allied form. 



I should regard the Phreodrilidse as a very low form of Oligochseta greatly 

 specialised in certain directions. I should explain, however, that in using the expression 

 " low," I do not mean that this genus is in any way near the ancestral form of the 

 Oligochseta. The simplicity of structure in this and other aquatic genera is rather to 

 be looked upon as evidence of degeneration. The almost complete ciliation of the 

 alimentary tract is a feature that Phreodrilus shares with the simpler forms ; so also is 

 the very complete internal metamerism of the body ; I mean as regards the interseg- 

 mental septa. Whether it actually propagates by the asexual method, is a question upon 

 which I may possibly have the opportunity of reporting later ; but I am in the mean- 

 time inclined to suspect that Phreodrilus will prove to be one of the " Gemmipares" 

 of d'UDEKEM. Another character by which Phreodrilus shows its low position among 

 the Oligochseta is the absence of spermsacs or ovisacs. There are some indications, to 

 which I have duly referred above (p. 267), that an egg sac is formed by a dragging back 

 of the septum bounding posteriorly segment XII. However, in the not fully mature 

 Stylaria lacustris, Vejdovsky figures (7, pi. iv. fig 2, v.) an egg sac totally distinct from 

 the septa, and apparently bearing no relation to them. On the other hand, in Mesen- 

 chytrceus there is an impaired egg sac very like that of Phreodrilus, but longer. 

 Whatever may be the case as regards the egg sac in specimens of Phreodrilus with 

 more matured female sexual organs than my example, it appears highly probable that 

 a sperm sac is never developed. 



I should place the Phreodrilidse nearer to the Naidomorpha than to any other group 

 of Oligochseta, though I admit that the position of the genital organs suggests an 

 affinity to the Enchytrseidse. But what their exact position with regard to these lower 

 groups is, I regard as a matter which cannot be at present satisfactorily determined. 

 There are, however, a few points in which Phreodrilus recalls the higher among the 



