THE NEPHRIDIUM OP LUMBRIOUS. 321 



vessels which twine amongst themselves and between and 

 around the tube of the nephridium (fig. 3). 



Although the existence of this elaborate blood-supply has 

 long been known (for instance, Morren describes it), and was 

 indeed adopted by Claparede as one of the distinctive cha- 

 racters of earthworms as opposed to water-worms, yet no 

 drawing or detailed description appears to have been pub- 

 lished. 



The remarkable dilatations of the blood-vessels here and 

 there were observed by Williams long years ago ; they re- 

 ceived further attention from Lankester and from d^Udekem, 

 who figured them (31, pi. iii, fig. 27), and a little later from 

 Claparede (16). In Pontodrilus, Perrier (27, pi. xvii, fig. 

 35) observed them; and in Diachseta, I pictured them (9, 

 pi. ix, figs. 35, 36). 



It is to be noted that these dilatations are by no means 

 constantly present in every earthworm. I have frequently 

 examined dozens of nephridia from one specimen of Lum- 

 bricus, and seen no dilatations whatever (as fig. 22) ; whilst 

 in other specimens examined at the same time, from the 

 same locality, and apparently in the same sexual condition, I 

 have seen these dilatations in abundance. But, again, not 

 every nephridium in the same worm presents this character ; 

 in some they are rare, in other nephridia they are altogether 

 absent. 



As is well known, they occur not only on the nephridia, but 

 on the septa ; and are, as Claparede figured, usually filled with 

 corpuscles (as in PI. XXIV, fig. 18). 



The cause of their appearance and the use of them to the 

 worm is a matter, at present, of speculation. Gegenbaur (19) 

 noted them and their inconstancy, and suggested that they 

 are present when the gonads are fully ripe ; but they seem to 

 be independent of this condition. 



Another peculiar phenomenon is sometimes to be seen in 

 the blood-vessels in the nephridium ; the colour of the blood, 

 instead of being pale yellow, as is normally the case, is more 

 distinctly red — a pinkish red — comparable to the colour of 



