CHAP. VIII.] LIKENESSES IN ANIMALS AND PLANTS. 265 



First, as to comparative anatomy, one example may be 

 selected where others can be easily adduced, if ^ 



Evidences 



required. fromcom- 



parative 



On the hypothesis of evolution, tortoises must be anatom y- 

 reckoned as very far indeed from being the first and earliest 

 kinds of quadrupeds. Yet, certain tortoises exhibit the 

 most extraordinary resemblance and correspondence between 

 their anterior and posterior limbs. This degree of likeness 

 and correspondence, then, must be the effect of a spon 

 taneous development, and cannot be merely due to inherit 

 ance, because it does not exist in other forms which, upon 

 evolutionary principles, are more nearly related to the 

 hypothetical root-forms. 



As to teratology, it is notorious that serially homologous 

 parts tend to be similarly affected great toes shar- From tera . 

 ing abnormalities of structure with thumbs, and tology - 

 ankles with wrists, knees with elbows, and so on. Professor 

 Burt Wilder has recorded six cases in which both the little 

 fingers and both the little toes were similarly affected, and one 

 case in which serial symmetry was alone exhibited, the right 

 little finger and the right little toe being the only ones 

 affected. But perhaps the most curious and instructive 

 instances are those in which the feet of pigeons or fowls are 

 abnormally feathered, or, as it is termed, furnished with 

 &quot;boots.&quot; These extra feathers are developed along the 

 very parts of the foot which correspond to (i.e., are serially 

 homologous with) those parts of the bird s hand which bear 

 the wing-feathers, so that these &quot; boots &quot; are plainly a serial 

 repetition of the true wing-feathers. These foot-feathers 

 have, indeed, been sometimes proved to exceed the wing- 

 feathers in length. Moreover, the foot-feathers resemble 

 the true wing-feathers in structure, and are quite unlike the 

 down which naturally clothes the legs of such birds as 

 grouse and owls. But there is a more striking correspond 

 ence still, for in pigeons which are thus &quot; booted &quot; the two 



* For others, see Genesis of Species, chap. viii. 



