Currents in Pholas and Mya. 371 



gical Society*/ and more in detail in Charlesworth's ' Magazine 

 of Natural History f/ after describing the structure of those 

 genera in which the water is acknowledged to flow in by the 

 branchial siphon, and to be discharged by the anal one, goes on 

 to say that u in the Solen, Hiatella, Mya, Pholas, Teredo, &c, a 

 different disposition takes place. Here the branchiae are pro- 

 longed into the inferior siphon, and as they are not separated 

 from the base of the foot within, nor from the mantle without, 

 the water drawn through the inferior orifice must make its exit 

 by the same or by the anterior opening. But water is also drawn 

 in by the other, and so gets access to the interior interlamellar 

 spaces of the branch ise ; and by this superior siphon, ova, faeces, 

 and secretions are discharged." From the statement here made 

 it would appear that Mr. Garner draws his inferences from the 

 anatomy of the animal alone, and not from actual observation of 

 the currents, as he seems doubtful whether the water received by 

 the branchial siphon is discharged by the same orifice or by the 

 anterior opening. 



Mr. Clark, however, has gone much further than Mr. Garner 

 in an attempt to establish a somewhat similar view of the sub- 

 ject. By a series of experiments with mercurial injections, in- 

 troduced principally through the anal siphon, he claims to have 

 proved that no communication can exist between it and the 

 branchial cavity ; and by other experiments upon the living ani- 

 mal, that gentleman announces that he has made a most import- 

 ant discovery, namely : — that " nine-tenths, if not all, the water 

 to bathe the branchiae is admitted by the pedal gape, and ejected 

 only by the branchial siphon ; the anal one alone inhales water 

 and discharges it ;" and that " in the close-mantle Solenidce, 

 Myada, Lutrarice, &c, as well as in the open-mantle Veneres, 

 Cardia, &c, the water is only admitted into the branchial vault 

 at the pedal or ventral aperture by the simple opening of the 

 valves, and ejected, according to the structure of their respective 

 sacs, either by the branchial issue alone, as in the Pholades, &c, 

 or as in the Veneres, Cardia, &c, by the two confluent orifices, 

 which are in fact but one branchial conduit." 



This conclusion, so contrary to the experience of other natu- 

 ralists, has been deduced from the following experiment. A 

 Pholas, inflated with water, was lifted up and held in an inverted 

 position with the siphons downwards, until all the water had run 

 out. More water of course ran out of the branchial than the anal 

 siphon, as might have been inferred from its larger aperture, the 

 absence of a valve, and its more direct communication with the 

 branchial cavity, in which the principal part of the water is con- 



* Vol. ii. p. 91. t Vol. iii. 



24* 



