262 Likenesses; or, Philosophical Anatomy 



the new oral expression. We have to thank Professor Ray 

 Lankester for the introduction of the terms ' homoplasy ' and 

 ' homoplast/ to express such uninherited resemblance and 

 such resembling parts, as well as for the antithetical terms 

 ' homogeny ' and ' homogen/ to express inherited resemblance 

 and the parts which manifested it. 



For our part, experience more and more convinces us 

 that the number of similarities which have arisen independ- 

 ently {i.e. cases of homoplasy) is prodigious, as well as that 

 very great caution is needed in endeavouring to discriminate 

 between likenesses which may be due to inheritance, and 

 those which are due to some other cause. The wonderfully 

 minute, exact, and elaborate investigations of the first of 

 our English embryologists (the late Professor Parker) con- 

 stantly made manifest the existence of an apparently in- 

 exhaustible number of complex cross relations between 

 widely different animals, and show more and more plainly 

 the entangled interdependencies of their structure. The 

 notion, once popular with evolutionists, that 'similarity 

 of structure' necessarily impHes 'genetic affinity,' can 

 certainly now be maintained, as a biological axiom, by no 

 well-informed naturalist. 



Indeed, the distinction between homogeny and homoplasy 

 (between the influence of a common descent and that which 

 produces independent similarity) has its importance much 

 reduced through the power which the latter possesses of 

 simulating the former. The degree to which homoplasy 

 can rival homogeny in the degree of likeness produced, is 

 shown, not only by the instances cited, but also by the 

 likenesses existing between some of the bones of the skull 

 in beasts and in osseous fishes. Probably but few naturahsts 

 would now dispute the independent origin of the bones of 

 the skull in those two classes of animals. Yet their cranial 

 bones are in many instances indisputably homologous, 



