Prof. Marignac on Atomic Volume and Specific Gravity, 527 



parts of the body, to different animals; but I have been in the 

 habit for some years past, of expressing this kind of analogy 

 by the term 'homology;' and I heartily join in the recom- 

 mendation of your ingenious correspondent, that all writers 

 on comparative anatomy and zoology should use the word in 

 that sense, whether it be or be not coupled with the likeness 

 of function performed by such parts ; to signify which rela- 

 tion alone, the term ' analogy ' should be restricted. As in- 

 stances of parts both homologous and analogous, may be 

 cited the pectoral limb of the Porpoise and that of the Fish : 

 they are homologous as being constituted of essentially the 

 same or corresponding parts ; they are analogous as having 

 the same relation of subserviency to swimming. So likewise 

 the pectoral fin of the flying-fish is analogous to the wing of 

 the bird; but, unlike the wing of the Dragon, it is also homo- 

 logous with it. Some organs are analogous, but only par- 

 tially homologous: thus the Monkey's foot is analogous to the 

 Man's hand, as having the functions of the opposable thumb : 

 it is also homologous with it generally, as being part of the 

 radiated appendage of a haemal arch ; and serially as being 

 the terminal segment of that appendage; but it is not specially 

 homologous with it. The thumbless hand of si teles is spe- 

 cially homologous with the perfect hand of Man, but the polli- 

 cate foot of Ateles is not so. I offer these as examples of the 

 mode in which ' homology * ' is illustrated in my own Lectures 

 on Comparative Anatomy, in addition to those cited from my 

 printed works. 



I am, Gentlemen, 

 College of Surgeons, Youi * most obedient Servant, 



May 9, 1846. RlCHARD OwEN. 



LXXX. Observations on Messrs. Lyon Playfair and Joule's 

 Memoir on Atomic Volume and Specific Gravity. By Prof 

 Marignac of Geneva\. 



HPHE authors in this paper have determined the density 

 — of a large number of bodies, and have arrived, by a com- 

 parison of their atomic volumes, at laws which would be rather 

 curious if they could be regarded as proved. Their investi- 

 gations have been principally directed to the soluble salts, and 

 they have sought to determine not only the atomic volume of 



* In geometry those sides of similar figures which are opposite to equal 

 and corresponding angles are sometimes said to be homologous, as being 

 proportional to each other. 



f Translated from the Bibllothequc UniverseUe. Feb. 15,1846. The 

 memoir referred to will be found at p. 453 of the previous volume of this 

 Journal. [Ed. F hit. Mag.] 



