454 Mr. W. Clark on the Animal of Kellia rubra. 



which it entered, which is effected by the internal communica- 

 tion before mentioned between the two at their bases, the stream 

 flowing smoothly out of the branchial one, and from the anal 

 conduit, more or less irregularly as the animal opens or closes the 

 hyaline valve, usually, if not always, found at its terminus. 



A careful investigation of cause and effect, in these mollusca 

 so difficult of examination, often produces a more satisfactory 

 elucidation of facts than even the demonstrations resulting from 

 the scalpel, which are often deceptive, erroneous and conflicting. 



For these reasons the doctrine of the apertures of inhalation 

 and exhalation being '^ kept distinct," or, in other words, that 

 when the water is received by one duct it is discharged by 

 another, is, I think, untenable. 



Mr. Alder says, he saw, under the power of the microscope, a 

 continuous current of water flowing into the anterior tube of 

 Kellia rubra ; all must admit this fact : as the fold is part of the 

 open mantle, no microscope is here required, as in every open- 

 mantled bivalve of adequate size this action is instantly made 

 apparent by a common lens, and is the invariable result of the 

 animal opening its valves; but that the most accomplished ob- 

 server by the microscope can, with any certainty, detect in so 

 minute a branchial slit as that of Kellia rubra, the entrance or 

 egress of branchial currents, is to me a matter of the gravest dif- 

 ficulty, which I can only get over, not by doubting the perfect 

 integrity of Mr. Alder's statement, but by supposing he may 

 possibly be in error, and has been misled by the aberration and 

 well-known great deceptions involved in the use of high micro- 

 scopic powers. 



But, for argument, we will assume that the posterior branchial 

 slit, as Mr. Alder states, showed no signs of an ingress current. 

 The contrary fact is, I think, proved by the contraction and 

 dilatation of the slit ; which action Mr. Alder admits, but says 

 that it has '^ no power to produce the internal circulation, but 

 merely to regulate the discharge." Surely the more reasonable 

 assumption is, that the periodic opening and closing of the aper- 

 ture is for the ingress and egress of part of the water for 

 branchial uses; especially as I have shown that the analogous 

 tubes of the close-mantled mollusca, — the anal one having, I be- 

 lieve, always at its terminus a hyaline contractile and expansive 

 valve, which appendage the branchial one is sometimes provided 

 with, — must of necessity receive and discharge the fluid necessary 

 for the branchial oeconomy. 



As another, and the last proof I shall adduce, that the bran- 

 chial slit, or aperture, in Kellia rubra, is not only for egress, 

 agreeably to Mr. Alder's opinion, but is also one of ingress, ac- 

 cording to mine, may be thus shown. Suppose Kellia rubra, 



