264 LESSONS FKOM NATUKE. [CHAP. VIII. 



gonj as, e.g., the nail of a man s middle toe and the hoof of 

 a horse s hind foot. 



15. General homologues, which are parts belonging to 

 the same general skeletal category as, e.g., when we say of a 

 part that it is a limb, or of another that it is a rib, or of 

 a third that it is a vertebra. We may distinguish then 

 different kinds and degrees of relationship, which are 

 severally perceived according as the mind is directed along 

 one line of inquiry or another, and whether concerning 

 different individuals or different parts of the same indi 

 vidual. 



Now I contend that it is against reason to suppose 

 Not due to that mere indefinite variation, together with the 



the survival i p -\ r&amp;gt; 11 i 1-1 



of the attest. &quot; survival oi the nttest, could ever have built 

 up all these serial, lateral, and other homologues without 

 the action of some innate power or tendency so to build up 

 possessed by the organism itself in each case. 



What can be more wonderful than the symmetry of those 

 lowly but beautiful organisms, the Acanthometree a sym 

 metry for which it is difficult to conceive any external 

 cause. Hardly, if at all, less wonderful is the radial sym 

 metry of the Echinoderms (the sea-stars, sea-eggs, and sea- 

 urchins) with their multitudinous variety of component 

 parts. If, then, internal forces can build up such varied 

 structures as these, they may well be also capable of pro 

 ducing the various serial, lateral, and vertical symmetries 

 which higher animals exhibit. 



We may next consider whether there are not other ex 

 ternal evidences (besides the homologues themselves) of the 

 existence of such an internal power, by the action of which 

 these recondite &quot; likenesses &quot; may be conceived to be brought 

 about. It is here contended that there is good evidence of 

 the existence of some such special internal power, which 

 evidence may be gathered from three sources : 1, Compara 

 tive anatomy; 2, the science of monstrous births, or tera 

 tology; and 3, the science of diseased structures, or pa 

 thology. 



