Mr, J. Alder on the Animal of Kellia rubra. 49 



found myself in agreement. Our opinions, however, appear to 

 differ more widely that I at first expected. 



In my last letter I ventured to lay down, perhaps more broadly 

 than usual, the theory of the branchial currents in the Conchifera 

 as generally received*; and confirmed, as far as my experience 

 goes, by my own observations. This theory of ciliary currents, 

 received and expelled by separate apertures, Mr. Clark entirely 

 denies, and thinks, if I understand him rightly, that no apertures 

 are specially set apart for this purpose, but that the water for 

 branchial purposes flows in and out of all the openings of the 

 mantle indiscriminately ; — whether by ciliary action or not, is not 

 stated. 



To enter into a review of this process as applied to the whole 

 of the bivalves would greatly extend a discussion already, I am 

 afraid, encroaching too much upon your pages ; and as I do not 

 feel that I shall be able to throw any new light upon it from my 

 own observations, I shall waive the general subject for the pre- 

 sent and confine myself to the consideration of Mr. Clark's ob- 

 jections to my views on Kellia rubra, which he thinks it not dif- 

 ficult to show are wrong. Let us, then, carefully examine the 

 arguments by which this position is to be established. 



The first is thus stated : — " It must be borne in mind that the 

 mantle of Kellia rubra is open from the posterior branchial slit 

 to its anterior termination. The open fold in question is merely 

 a prolongation of that membrane ; and when the animal opens 

 its valves f, it must receive, like the Mactrce and Veneres, or any 

 other bivalve with an open mantle, the currents of sea- water ; and 

 in closing them, a great part thereof, after bathing the branchiae, 

 is ejected from the aperture of ingress, and only a portion of it 

 passes out of the posterior orifices." This I admit to be the 

 natural effect of the opening and closing of the valves, but surely 

 Mr. Clark does not mean to say that the branchial currents are 

 produced by this means ? According to my views this is an oc- 

 casional action entirely independent of the regular branchial cur- 

 rents, and should not be confounded with them, as these latter 

 go on when the valves are entirely at rest, and when consequently 

 no such effect as here described could possibly be produced by 

 them. As to the siphonal fold being merely a prolongation of 

 the mantle, this is the case with the siphons of all the Conchifera ; 

 the only difference being, that in the present instance the tube 

 is formed by a fold of the mantle, while in other genera, and in 



* See Lamarck, Anim. s. Vert. 2nd ed. vol. vi. p. 7 ; Grant, Comp. Anat. 

 p. 539 ; Owen, Lectures on Comp. Anat. vol. i. p. 282. 



t These words are here put in italics, though not so in Mr. Clark's letter, 

 to draw particular attention to them. I have taken the liberty of doing the 

 same in other places. 



Ann. &; Mag. N. Mist. Ser. 2. Vol. iv. 4 



