CRITERIA OF HOMOLOGY 167 



if a membrane bone is found in the position ordinarily 

 occupied by a cartilage bone, is it to be regarded merely 

 as the analogue and not as the homologue of the latter ? " 

 (p: 296). 



We may note here that many comparative anatomists of 

 the period were quite ready to decide Huxley's last question 

 in a sense favourable to the older, purely anatomical, view 

 of homology. Owen, for instance, held that difference of 

 development did not disturb homologies established by 

 form and connections. " Parts are homologous," he writes, 

 " in the sense in which the term is used in this work, which 

 are not always similarly developed : thus the ' pars occipitalis 

 stricte dicta,' etc., of Soemmering is the special homologue of 

 the supraoccipital bone of the cod, although it is developed 

 out of pre-existing cartilage in the fish and out of aponeurotic 

 membrane in the human subject." 1 Similarly he pointed to 

 the diversities of development of the vertebral centrum in 

 the different vertebrate classes as proof that development 

 could not always be relied upon in deciding homologies 

 (p. 89). But he could not deny that the archetype was better 

 shown in the embryo than in the adult (supra, p. 108). 



J. V. Carus ' 2 likewise stood firm for the older method of 

 determining homologies by comparison of adult structure. 

 " We can regard as homologous," he writes, " only those 

 parts which in the fully formed animal possess a like 

 position and show the same topographical relations to the 

 neighbouring parts" (p. 389). Parts homologous in this sense 

 might develop in different ways, but no great importance was 

 to be attached to such a circumstance. Membrane and 

 cartilage bones developed in practically the same way, from 

 the same skeleton-forming layer, and no morphological 

 significance attached to their distinction (pp. 227, 457). 

 Embryology was of considerable value in helping to 

 determine homologies, but the evidence that it supplied was 

 contributory, not conclusive. Perhaps the greatest service 

 which the study of development rendered was to disentangle, 

 by a comparison of the earliest embryos, the generalised 

 type (p. 389). 



1 On the Archetype of the Vertebrate Skeleton, p. 5, 1848. 

 * System der thierischen Morphologic, Leipzig, 1853. 



M 



