APPARENT EXCEPTIONS. 211 



the Unity of Design, the other represents Va- 

 riety of Function. It might have been supposed 

 that these could not easily be reconciled — that 

 where great differences in use and application are 

 essential, rigid adherence to one pattern of struc- 

 ture would be an impediment in the way. But it 

 is not so. The same bones in different animals 

 are made subservient to the widest possible diver- 

 sity of function. The same limbs are converted 

 into paddles, and wings, and legs, and arms. And 

 so it is with every other part of the skeleton and 

 every other organ of the body. Indeed it is diffi- 

 cult to say whether the law of unity in design, or 

 the law of variety in adaptation, is pushed to the 

 greatest length. There are some cases in which the 

 adaptation of form to special function is carried 

 so far that all appearance of common structure 

 is entirely lost. It is very difficult, for example, 

 to persuade persons ignorant of the principles 

 of anatomy that the Whale and the Porpoise are 

 not Fish, that they breathe with lungs as Man 

 breathes, that they would be drowned if kept long 

 under water, and that as they suckle their young 

 they belong to the same great Class, Mammalia. 



