n6 SIR WILLIAM FLOWER CHAP. 



the ridges are larger, as in the dog, pig, etc. In No. 4 they are 

 still larger, and develop conical papillae on their free surface, as 

 in the ox and giraffe (the "forked" end of the lamina is only 

 diagrammatical, as it is impossible in such a view to show a view 

 of papillae side by side along the edge). In No. 4 we see the 

 evolution of whalebone in its simpler forms the ridges or lamina 

 longer, the papillae greatly extended, and the epithelial covering 

 " mere differentiations of a continuous but not very conspicuous 

 epiplastic thickening, which is probably the rudiment of a lateral 

 fin." In the chick " the limbs appear as outgrowths from a 

 slightly marked lateral ridge which runs on the level of the lower 

 end of the muscle plates for nearly the whole length of the 

 trunk." 



The progress of development of an organ before it becomes of 

 actual use to its possessor always seems to me one of the great 

 difficulties in endeavouring to account for such progress by the 

 principle of natural selection alone ; such rudimentary limbs, 

 however, mere flaps of skin, would, especially when muscles are 

 developed within them, soon aid in progression through the water, 

 and then might become defined in form, and strengthened by the 

 growth of supporting structures within, first as mere fin rays, 

 afterwards extending inwards as the bones which connect the 

 outer part of the limb to the axial skeleton. This is my idea of 

 the process of growth or development of the limb of a vertebrate 

 animal, and it is pretty well borne out by what we see in the 

 adult condition of many fishes which possess the distant but not 

 the proximate part of the member the reverse condition to that 

 of the whales. 



THE DUKE OF ARGYLL TO PROFESSOR FLOWER 



INVERARAY, January 13, 1884. 



1 write a line to congratulate you on your removal to a wider 

 sphere of usefulness, a change in which the public will gain more 

 largely than yourself. 1 I have been reading over again your lecture 

 on whales. I recollect when I first asked you the question 



1 His appointment as Director of the Natural History Museum. See 

 next chapter. 



