Body Covering 17 



us, they open at their ends and let the blood escape into 

 open spaces, to find its way back to the heart as best it can. 



In the fish, the situation is different. The fish has the 

 same systems which the invertebrate has, but the organs 

 which make up these systems are different. They are for 

 the most part remarkably similar to the corresponding organs 

 in mammals. They are simpler, but they work on the same 

 principles. They might be likened to earlier models of the 

 same machine, accomplishing the result in the same way, 

 but less adequately and less efficiently, just as the single- 

 tube radio worked on the same principles as the most up-to- 

 date multi-tube superheterodyne. 



Like the owner of the primitive radio, the fish is limited 

 in his range of interests by the imperfections of his machinery. 

 He concentrates on food, shelter from danger, and a mate. 

 He leads a simple, straightforward life, and his organs are 

 adapted to the life he leads. Or, as the mutationists would 

 say, the life he leads is adapted to the kind of organs he has. 



SKIN 



The first organ system to be met in an orderly examina- 

 tion is the body covering. This system is the most striking 

 instance which we shall find of the fish doing things dif- 

 ferently from the mammals, and for once in a more com- 

 plicated way. 



In the first place, the fish's skin is alive. The very outer- 

 most covering, the covering which comes in contact with 

 the great world, is composed of living cells. This is not the 

 case with us, for the living part of our skin is covered with 

 several layers of hardened cells which, although transparent, 

 are completely dead. They protect the living cells under- 

 neath. When you touch another human being, you do not 

 come in contact with living flesh — unless you are a dentist, 

 when, if you are a little clumsy, the dead skin of your finger 



