241 



above the general level is sensibly neutralized by the deficiency of 

 attraction below it where the lighter crust displaces the heavier lava. 

 In like manner, the horizontal attraction of a ship or other floating 

 body is nothing. But the horizontal attraction upon a near point 

 on the earth's surface will not vanish, because the mountain which 

 produces the positive attraction is nearer than the lava-displacement 

 which produces the negative attraction : even here, however, the 

 efficient disturbing attraction will be much less than that computed 

 by considering the dimensions of the mountain only. 



III. Note to a paper entitled " Contributions to the Anatomy of 

 the Brachiopoda/' read June 15, 1854. By THOMAS 

 H. HUXLEY, Esq., F.R.S. Received February 12, 1855. 



My attention having been called within the last two or three days, 

 o an error in my paper on the Anatomy of the Brachiopoda, 

 published in No. 5 of the Royal Society's Proceedings, I beg to be 

 allowed to take the earliest opportunity of correcting it. At p. Ill 

 of that paper the following paragraph will be found : 

 - " In 1843, however, M. Vogt's elaborate Memoir on Lingula ap- 

 peared, in which the true complex structure of the 'heart' in this 

 genus was first explained and the plaited ' auricle ' discriminated 

 from the ' ventricle ;' and in 1845, Professor Owen, having appa- 

 rently been thus led to re-examine the circulatory organs of the Bra- 

 chiopoda," &c. &c. 



Now, in point of fact, though M. Vogt does describe and accu- 

 rately figure the structures called ' auricle ' and ' ventricle ' in Lin- 

 gula*, yet he has not only entirely omitted to perceive their con- 

 nexion, or to indicate the ' auricular ' nature of the former, but he 

 expressly states that the so-called ' hearts' are " simple, delicate, pyri- 

 form sacs" (p. 13). 



I presume that my recollection of M. Vogt's figures was more 

 vivid than that of his text ; for having been unable, notwithstanding 

 repeated endeavours, to re-obtain the memoir when writing my paper, 



* Neue Denkschriften der allgemeinen Schweizerischen Gesellschaft fur die 

 gesammten Naturwissenschaften. Band VII. 



VOL. VII. 2 B 



