DESCRIPTIONS OF GENERA AND SPECIES 179 



in certain species of Aeolosoma. The coelom is of course lined by peritoneum, 

 and contains a few round corpuscles, which vary in number at different times. 

 There are no dorsal-pores and no head-pore ; the coelom, however, communicates 

 with the exterior by the 



Nephridia. These organs are paired and metamerically arranged. They commence 

 at earliest behind the first bundles of setae ; we might possibly, therefore, consider 

 that they belong to the third segment, were it not for the position of the funnel ; 

 the definite location of the nephridia is, however, rendered impossible by the 

 absence of the septa separating the segments ; VEJDOVSKY considers that the first 

 pair of nephridia belong to the second (i.e. the first setigerous) segment. In this 

 case the entire nephridium is confined to a segment, for the funnel does not 

 perforate the only existing septum, that dividing segments i and ii. The fact 

 that the external pore of the nephridium (in A. headleyi at any rate) lies in 

 advance of the funnel 1 is a further confirmation of VEJDOVSKY'S suggestion. In 

 A. variegatum the first nephridium is in segment iii. The nephridium is attached 

 by a delicate muscular band to the gut ; each is a much-coiled tube, with 

 granular nucleated walls. STOLC has figured (1, PI. vii. fig. 4 a) a peritoneal 

 covering of transparent vesicular cells ; the ciliated funnel is composed of very 

 few cells ; it is hardly wider than the tube which follows. Just before the 

 external pore, which lies ventrally in front of, and to the inside of, the ventral 

 setae-bundles, the nephridium dilates into a clear-walled vesicle, which VEJDOVSKY 

 states to be contractile, and to be filled with a clear fluid. 



During sexual maturity some of the nephridia, as Dr. STOLC discovered (1), 

 disappear ; the others, particularly those of the sixth segment, convey the sperm to 

 the exterior ; in the sixth segment one nephridium only is figured by STOLC (1, 

 PI. vii. figs. 2, 3 e c h) ; this is larger than the rest, and the funnel, instead of facing 

 backwards, as in the other nephridia. faces forwards. It also appeal's to be shorter. 



VEJDOVSKY discovered that in the buds of Aeolosoma the first segment is 

 provided with a pair of provisional nephridia. These organs were chiefly studied in 

 A. tenebrarum ; they are most evident in the head segment, before the pharyngeal 

 ingrowth has taken place, while the gut is still continuous from the parent worm 

 to the bud ; they lie closer to the gut on either side, and each consists of a thick- 

 walled, hollow sac, of a pear-shaped outline ; the narrow end of this sac is attached to 

 the dorsal body-wall, but no orifice leading to the exterior could be discovered ; nor 

 is there any coelomic aperture. They disappear on the invagination of the pharynx. 



1 STOLC, on the other hand (1), figures the funnel as in advance of the external pore ; the relative 

 position of the two, however, undergoes constant change owing to the movements of the worm. 



,\ a 2 



