EXCURSIONS OF AN EVOLUTIONIST 



that the arms of men, the fore-legs of quad- 

 rupeds, the paddles of cetacea, the wings of birds, 

 and the pectoral fins of fishes should be struc- 

 turally identical with one another. It is intelli- 

 gible that a horse's hoof should be, as it is, made 

 up of toes that have grown together. It is intel- 

 ligible that every mammalian embryo should be- 

 gin, as it does, to develop as if it were going to 

 become a fish, circulating its blood through gills 

 and a two-chambered heart, and then, changing 

 its course, should behave as if it were going to 

 become a reptile or bird, and only after long 

 delay should assume the distinctive characteris- 

 tics of mammality. It is intelligible that many 

 snakes should possess beneath their skin the 

 rudiments of limbs ; that sundry insects, which 

 never fly, should have wings firmly fastened 

 down to their sides ; and that the embryos of 

 many birds, while developing in the egg, should 

 grow temporary teeth within their little beaks. 

 But it is only on the theory of " descent with 

 modifications " that such facts, which are in no 

 wise exceptional, but common throughout the 

 entire animal kingdom, have any meaning what- 

 ever. 



Many of these facts had been noticed by em- 

 inent naturalists before Mr. Darwin, and their 

 incompatibility with any theory of special crea- 

 tions had also been observed ; but it was Mr. 

 Darwin who first marshalled them into one 

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