1 86 SCIENCE SKETCHES. 



conceive it to be true of man also. That it is in 

 fact true of man, we know ; for not many thousands 

 of years ago our ancestors in Europe were bar- 

 barians, cave-dwellers, lake-dwellers, and dwellers 

 in hollow trees, with only the rude implements 

 they shaped from metal and flint. Surprisingly 

 like us in form and structure, though far below us 

 in skill and intelligence, are the many races of 

 apes and monkeys. And among these, or rather 

 behind these, for these too are changing with the 

 changing conditions of life, must our ancestry be 

 traced. 



If anything is certain in science, it is this. What 

 we call homology represents something real, some 

 law of Nature, something other than the results 

 of mere chance. When I compare my arm with 

 that of my neighbor, I find some differences, — 

 differences in size, in proportions. But these are 

 superficial, and there is the underlying corre- 

 spondence of each bone and muscle, each nerve- 

 fibre, artery, and vein. When I compare my arm 

 with the foreleg of a dog, I find more striking 

 differences, for the dog's station in life is quite 

 unlike my own, and his arm he uses for quite dif- 

 ferent purposes. When I compare my arm with 

 the wing of a bird, or the pectoral fin of a fish, 

 the results are still similar. Though the differ- 

 ences in each case become more and more strik- 

 ing, and the resemblances less easy to trace, yet 

 the same resemblances exist, and a closer study 

 shows that these resemblances far outweigh the 

 differences. 



We say, then, that homology is real, and what- 



