386 W. BLAXLAND BENHAM. 



is no trace of the other nephridia. It will be an interesting 

 point to look for in the developmental history of the genus — 

 the suppression of nephridia ; for Michaelsen has described 

 certain earthworms, Kynotus, in which the nephridia are 

 stated to occur in alternate somites. I have suggested else- 

 where that an error in observation may perhaps have occurred, 

 and that the external markings indicating '^ somites " are 

 in reality annuli. But in Naid, of course, there is no question 

 of annuli. 



The first nephridium lies in Somite vii ; the arrangement in 

 following somites is subject to a good deal of variation. 



The post-septal glandular region of the tube is of a different 

 shape from that figured by Vejdovsky for N. elinguis, and 

 more nearly resembles therein N. josinse (Vej., pi. iii, fig. 4, a); 

 but with regard to the terminal dilatation this species differs 

 considerably from N. heterochseta (cf. my fig. 4). 



EXPLANATION OF PLATE XXXIII, 



Illustrating Mr. W. Blaxland Benham's '' Note on a New 

 Species of the Genus Nais." 



Figs. 1—5 illustrate specific characters of Nais heterocbaeta, n. sp. 



Fig. 1. — The vascular system of the anterior somites. D. v. Dorsal trunk. 

 laL The two branches from the dorsal trunk which unite to form the ventral 

 trunk {V. v.). a, b, c, d. Vessels more or less branched, passing from dorsal 

 to lateral vessel, e. A commissural vessel from dorsal to ventral trunk, also 

 branched. 



Fig. 2. — A dorsal bundle of chaitse, consisting of one capilliform and one 

 furcate chseta. 



Fig. 3. — A ventral chseta. 



Fig. 4. — A nephridium, showing its extension into two somites, sept. 

 Septum, a. Granular post-septal region, b. Muscular (?) duct. /. Funnel. 



Fig. 5. — Brain, com. Origin of oesophageal commissure. 



