1 78 Mr. J. Alder on the Branchial Currents 



by Dr. Williams, which have appeared from time to time in your 

 Journal. That on the Mollusca, however, published last month, 

 contains some statements, which, as they are not founded on 

 fact, and are likely to be injurious to the scientific reputation of 

 a brother naturalist, I take the liberty of endeavouring to cor- 

 rect. I allude to the remarks on Mr. Hancock. Dr. Williams 

 gives that gentleman due credit for most of his investigations 

 into the mechanism of respiration in the Bivalves, but against 

 that praise he sets off certain errors which he alleges Mr. Han- 

 cock has committed, as follows : — " By Mr. Hancock, represent- 

 ing one class of observers, it is maintained that the inhalent 

 current is set in motion exclusively by the action of vibratile 

 cilia seated on the lining membrane of the siphon itself. By 

 Mr. Clark this explanation is denied. The former naturalist 

 rests his theory upon the alleged demonstration of cilia on the 

 internal surface of the inhalent siphon, the latter upon obser- 

 vation of the currents." " Mr. Hancock is undoubtedly in error 

 in stating that the water entering this cavity is drawn in by cilia 

 of the siphon. The microscope disproves completely the assertion 

 that the internal lining membrane of the inhalent or extra- 

 branchial siphon is the scene of ciliated epithelium." And con- 

 cerning the exhalent current it is stated, " The uninterruptedness 

 of this current was supposed by Mr. Hancock to be due to the 

 action of cilia lining the interior of the siphon. The statement 

 of this distinguished naturalist in this particular is indisputably 

 erroneous. This siphon, like the in-current one, is not lined with 

 vibratile epithelium." Again, we find it stated that " Mr. Han- 

 cock is inaccurate in affirming that all the water which enters 

 this cavity travels exclusively along the inhalent or extra-branchial 

 siphon, and never, under any circumstance, through either the 

 ventral or pedal openings." 



Mr. Hancock has made none of the statements here imputed 

 to him. The only place where any of his opinions concerning 

 these points are expressed is in a joint paper with myself, " On 

 the Branchial Currents in Pholas and Mya," read at the British 

 Association Meeting in 1851, and afterwards published in your 

 Journal*. Certainly no such statements are there made: indeed 

 the subject of cilia lining the siphons is not at all alluded to. 

 Dr. Williams, however, speaks of Mr. Hancock's controversy 

 with Mr. Clark, from which, and his not mentioning my name 

 in connexion with it, I am led to infer that he attributes to 

 Mr. Hancock a series of letters that I wrote in your Journal on 

 the subject. These letters bear my signature, and for anything 

 therein contained, I alone am responsible. Presuming that 



* 2nd Ser. vol. viii. p. 370. 



