STRUCTURE OF THE NEPHRIDIA OF DINOPHILUS. 535 



the basement membrane of the epidermis near the median 

 line on the ventral surface of the worm. On the course of 

 this portion of the nephridium the canal sometimes widens 

 into lacuna-like spaces in the living worm under compression. 

 A similar space is shown by Meyer (16) on all of the 

 nephridia in D. gy rociliatus (fig, 9). In the enlarged figure 

 (fig. 10) this space is again seen very much as it looks in D. 

 tseniatus (fig. 16) under compression. The walls of this 

 space are remarkably thin and uniform in thickness, and 

 have a transparent appearance, the masses of orange pigment 

 seen about the rest of the canal being usually wanting in the 

 walls of the spaces or lacunae. Through the middle of these 

 lacunfe the flagella, which, as I have mentioned, can be 

 traced down from the solenocytes, beat passing on and 

 through and down the nephridial canal (fig. 6). Meyer 

 shows these spaces lined with cilia. I think, however, they 

 are not so lined in D. tfeniatus, there being considerable 

 grounds for believing that the flagella beating in the spaces 

 where they spread out somewhat produce a false appeai*ance 

 of ciliation. It is difficult to describe this in some instances, 

 where these spaces, on the contrary, would seem to be 

 furnished with cilia. 



A more important difference between the canals of D. 

 gyrociliatus and D. tseniatus is that in D. tteniatus 

 they are never folded, as shown in Meyer's (16) fig. 10. The 

 lacunar appearance of these spaces is greatly increased by 

 the worms being under some compression when examined, 

 and they may be in great part produced by this compression. 

 While Meyer figures these spaces on all five pairs of 

 nephridia in D. gyrociliatus, I have observed them only 

 in one instance on the first nephridium and on the second, 

 but almost constantly on the third, in about five hundred 

 preparations examined altogether. Meyer (16) also shows a 

 well-marked external pore. It must be remembered that in 

 D. gyrociliatus, from Repiachoff's (21) figures and de- 

 scriptions, as well as in the two figures given by Meyer, the 

 body-cavity space is much better developed than in D. 



