258 



SCIENTIFIC THOUGHT. 



44. 

 Study of 

 homology. 



calary type." Especially through palseontological finds, 

 the landmarks were gradually removed which separated 

 the distinct species and groups of organised beings. 

 It had happened to Cuvier only in single instances 

 that he had to record resemblances between widely 

 separated groups. Such resemblances became more and 

 more frequent and perplexing. In the second place, 

 Owen had the great merit of giving more definite ex- 

 pression to the conception of analogies, as developed 

 principally by the school which Cuvier opposed. In 

 fact, he revised and brought into general use the term 

 " homology," which had already been used by French and 

 German anatomists before him.^ This term signified 



^ Great importance has been at- 

 tached to the term "homology," 

 which, to a reader uuiuitiated iu 

 the complicated and changing vo- 

 cabulary of the natural sciences, 

 presents not a little difficulty. 

 It is a good example of the 

 classical saying of Goethe, "dass 

 wo Begriffe fehlen, da stellt ein 

 Wort zu guter Zeit sich ein." In 

 the attempt to define the current 

 term "homology," in seeking for 

 numerous examples of homologies 

 as distinguished from analogies, nat- 

 uralists were led to the recognition 

 of i-eal, not only of verbal or logical 

 distinctions. In this respect it is 

 most instructive to read Owen's 

 treatise ' On the Archetype and 

 Homologies of the Vertebrate 

 Skeleton' (1848), the enlarged re- 

 print of a Report to the British 

 Association in 1846. In it he gives 

 a pretty full history of the term 

 homology, which in the first half of 

 the nineteenth century became cur- 

 rent with special meanings in three 

 independent sciences. With the 

 precision of the usage, both in 

 geometry and chemistry, the vague- 



ness of the term as used by nat- 

 uralists stands in characteristic con- 

 trast. " The corresponding parts," 

 Sir R. Owen there says (p. 5), 

 " in different animals being made 

 namesakes, are called technically 

 ' homologues.' The term is used 

 by logicians as synonymous with 

 'homonyms,' and by geometricians 

 as signifying ' the sides of similar 

 figures which are opposite to equal 

 and corresponding angles,' or to 

 parts having the same propor- 

 tions : it appears to have been 

 first applied in anatomy by the 

 philosophical cultivators of that 

 science in Germany. Geoffroy 

 Saint - Hilaire says, ' Les organes 

 des sens sont homologues, comme 

 s'exprimerait la philosophic Al- 

 lemande ; c'est-a-dire qu'ils sont 

 analogues dans leur mode de 

 develo2323ement, s'il existe veritable- 

 ment en eux uu meme principe de 

 formation, una tendance uniforme 

 li se rep^ter, h. se reproduire de la 

 meme fagon.'" After remarking 

 on the looseness of this definition, 

 Owen proceeds to give his own, 

 taken from the " Glossary " ap- 



