108 Mr. H, J. Carter on Microscopic Filaridse. 



to make any division of the oviduct in the lower ones, but to 

 call it after that part to which it comes nearest in the higher 

 animals, viz. the "fallopian tube/^ 



These worms, again, are too small to present any traces of a 

 vascular or nervous system, — at least I have not been able to 

 detect either in Urolabes palustris) nor have I been able to 

 ascertain how their respiratory functions are performed, beyond 

 the rhythmical influx and expulsion of water observed to take 

 place in the posterior uncovered part of the intestine (fig. 11 m), 

 through the anal orifice and rectum, as before stated. That this 

 takes place in the Naidina, and is produced there by the cilia 

 which cover the posterior part of the intestine, I have, since my 

 paper on the " Spermatology of Nais fusca '^ was published *, 

 been able to determine. In trying to account for the direction 

 in which the cilia lining the tube of the ^' segmental organ " 

 carried its contents, I observed that as these (viz. the faecal con- 

 tents in the posterior part of the intestine in the same Nais) 

 passed towards the anus, and thus against the direction of the 

 cilia^j so the direction of the cilia being outwards, or in the oppo- 

 site direction, in the " segmental organ" should indicate an in- 

 ward current through this organ,— that is, that the force of the 

 cilia was opposite to their apparent movement f. But since 

 then, I have, by placing some indigo in the water with another 

 species of Nais, observed that it was taken into the rectum and 

 some way up it, where it kept oscillating between the peristaltic 

 motion of the intestine and the cilia, until some faecal matter 

 arrived, when, by a forcible movement of the former, the whole 

 was expelled, and the indigo began to pass in again as before. 

 Thus the current of these cilia was satisfactorily proved to be in 

 the direction in which the cilia appeared to move ; and the direc- 

 tion of the movement of the cilia of the segmental organ being 

 outwards, would indicate an outward current in this organ. I 

 mention this more particularly to clear up the difficulty I then 

 had in speculating upon the probable function of the segmental 

 organ. Now in Urolabes palustr is there is nothing approaching 

 to a contracting vesicle or " segmental organ" in any part of 

 the body, and no evidence of water-respiration beyond that 

 which I have stated. That an aerating function of this kind is 

 performed by the posterior part of the alimentaiy canal of the 

 Naidina, is proved not only by what I have stated to occur in 

 the Nais on which the experiment of the indigo was made, and 

 by the existence of cilia on the posterior part of the intestine of 

 Nais fusca, but by the fact that in another species, like, if not 

 the same with Nais digitata, Gmel.J, which is common in Bom- 



* Annals, vol. xix. p. 20. f ]d. vol. xix. p. 28. 



X Encyclop. Meth. t. i. pi. 53. figs. 12-18. 



