98 SPECIES NOT 



undergone there in the production of animal 

 heat. I could point out how admirably adapted 

 is that exquisite organ, the lung, to perform 

 this function. How it is provided that on the 

 average at least twenty-six pounds of Llood 

 pass through these organs every three minutes 

 and a half of our existence, from the cradle to 

 the grave. How of this twenty-six pound? at 

 least one-sixth is composed of blood-discs, each 

 of which is only the three thousand two hundredth 

 part of an inch in diameter, and each of which 

 has to pass separately from artery to vein, and 

 along the capillaries every three minutes and a 

 half. And I could then ask the reader to fol- 

 low me down to fishes, where all traces of a 

 lung cease, and from them through the great 

 scale of living beings, in which there is not 

 only no vestige of a lung, but as we get lower 

 and lower, not even any vestige of a special 

 respiratory apparatus at all; and then, I might 

 triumphantly ask, where is the possibility that 

 this exquisite organ, the lung, could have been 

 produced by variation in beings in which not a 

 vestige of it existed? But all this would occupy 

 too much space, and I must therefore proceed 

 with one or two more illustrations of adaptive 

 design. 



Well then, there is a very obvious and beau- 

 tifuj instance of it which fell under my notice 

 while reading a few days ago researches into the 

 minute anatomy of the nervous system, by the 

 celebrated Van der Kolk. 



