CHAP. VIII.] LIKENESSES IN ANIMALS AND PLANTS. 261 



and a jumping mode of progression; yet this double similarity 

 is almost evidently induced and not inherited. The only 

 beasts of burthen known in South America when it was dis 

 covered by the Spaniards, were the Llamas, animals which 

 present a singular structure as to the course of their vertebral 

 arteries which pierce the neck-bones on their inner sides. 

 The very same condition, however, occurs again in the great 

 ant-eater, also an inhabitant of South America. Yet it is im 

 possible to believe that any special affinity, through descent, 

 can connect such strangely divergent forms. It is also note 

 worthy that this character can hardly have been due to any 

 action of &quot; natural or sexual selection.&quot; The examples cited 

 are but a few of many which might be adduced as evidence in 

 this matter. 



It is thus forced upon our attention (alike by the facts 

 of lateral and serial homology, as well as by Homopiasts 

 such as those just cited) that there are likenesses pusy. m&amp;lt; 

 or homologies which cannot be due to inheritance, and 

 which have to be distinguished from others which are, or 

 which may be, so flue. With the new mental conception 

 came, as was fitting, the new oral expression. We have to 

 thank Professor Kay Lankester for the introduction of the 

 terms &quot; homoplasy &quot; and &quot; homoplast,&quot; to express such 

 uninherited resemblance and such resembling parts, as well 

 as for the antithetical terms &quot; homogeny &quot; and &quot; homogen,&quot; 

 to express inherited resemblance and the parts which mani 

 fested it. 



For my part, experience more and more convinces me 

 that the number of similarities which have arisen inde 

 pendently (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 in 

 heritance, and those which are due to some other cause. 

 The elaborate investigations of the first of our English 

 embryologists (my friend Professor Parker), constantly 

 make manifest the existence of an apparently inexhaustible 

 number of complex cross relations between widely different 



