ME'I'AMEKIC segmentation and I1()M(3E0GY. 
227 
Metameric Segmentation and Homology. 
By 
Kflwiii S. F.K.S., 
Fellow of Merton College, Oxford, 
With Plates 15 and 16. 
In two recently published papers on the development of the 
fins of fish and on the segmentation of the head of Amphibia 
( 12 , 15 ), I had occasion to discuss incidentally the segmental 
relations of homologous organs, and to point out that, in the 
Vertebrates at all events, corresponding parts must be con- 
sidered as fully homologous although occupying different 
segments of the body. In this paper I shall not attempt to 
define the nature of segmentation nor trace its origin, but 
shall merely try to show that a practical definition of the 
homology of an organ must not depend on its position in the 
series of segments. The subject of metameric segmentation 
has been very clearly dealt with by Sir E. Ray Lankester in 
articles on the Arthropoda and Metamerism in the tenth and 
eleventh editions of the Encycloptedia Britannica^ (reprinted 
in vol. 47 of this journal). While giving a comprehensive 
review of the whole question of metamerism, he states thii teen 
laws,’^ or general propositions, with most of which what 
follows will be found in complete agreement. But, in spite 
of the results of Furbringer ( 9 , 10 ) from anatomical investi- 
gations, of Bateson ( 1 ) from observations on variation, and of 
others, there is, I think, a reluctance on the part of many 
anatomists to give up the idea that true homology depends 
on segmental correspondence. For instance, when discussing 
