28 Mr. II. J. Carter on the Spermatology of a new species of Nais. 



ticular direction manifested by the cilia of the internal open- 

 ing, while that of those in the tube is distinctly backwards, or 

 towards the external opening. What the direction of the con- 

 tents of the tube may be, I have not been able to determine, 

 for I have never seen anything pass through it; and the 

 floating-cells in contact with the internal opening indicate no 

 current at all, but merely displacement, when struck by the 

 cilia. No current can be seen, either, at the external opening, 

 when carmine is added to the water for ascertaining this ; but 

 the tube throughout becomes continually and gradually dis- 

 tended, and every now and then contracts suddenly, to empty 

 itself, after the manner of the contracting vesicle and its tubular 

 system in the Rotatoria and Infusoria, or perhaps, more parti- 

 cularly, in Lacinularia, where, according to Prof. Huxley, there 

 is no "contracting vesicle*." 



Of the use of this organ I am ignorant, but undoubtedly it is 

 homologous with the "contracting vesicle" and its tubular sy- 

 stem, both in the Rotatoria and many of the higher, if not in all 

 the Infusoria. In Nais fusca, no current, as just stated, appears 

 to pass into or out of either its internal or external orifice, 

 although there is a rapid ciliary movement going on throughout 

 the whole of the intervening tubular portion ; this motion again 

 appears to be from within outwards, from which it might be in- 

 ferred that the contents of the tube take the opposite direction, 

 and therefore that the fluid with which it becomes filled comes 

 from without. If we direct our attention to the cilia which 

 cover the rectal part of the intestine in N. fusca, &c, this move- 

 ment is evidently from behind forwards, while it is equally evi- 

 dent that the contents of the intestine pass in the opposite 

 direction ; and again, if we watch the cilia on the sides of a 

 Planaria, their motion will be observed to be towards the head, 

 while the current produced by them, as indicated by the neigh- 

 bouring particles, is distinctly backwards. This apparent con- 

 tradiction, however, appears to derive explanation from the 

 single cilium of some of the polymorphic Monads, which, undu- 

 lating from the base towards the extremity, draws the surround- 

 ing particles towards itself, and thus the motion appears one 

 way while the current is another f. Yet some of the larger 

 Rotatoria, in which the contracting vesicle is also very evident, 

 and opens freely into the cloaca, one would think ought to afford 

 us means of proving whether the fluid with which it becomes 

 distended really comes from within or without. I have, how- 

 ever, tried this, by placing carmine in the water with a large 

 species of Philodina, but never could detect any in the distended 



* Quart. Journ. Microscop. Soc. Lond. vol. i. p. 3, 1853. 

 t Annals, vol. x.\. pi. 1. %. 10. 



