Animal Evolution. 203 



discharging a current of electricity. This statement 

 is interesting in view of our magnetic and electric 

 hypotheses, unthought of as they are by the world of 

 science at present. 



The wings of birds are also perfectly adapted to 

 their purpose. The feathers are both strong and 

 light, yielding at the upstroke but rigid in the down. 

 Organic conditions have, however, accorded to the 

 bird less efficient pinions than the insect, for the 

 broad end of the wing in birds is nearest the body 

 instead of outermost as in insects. But more power- 

 ful muscles are required to work the latter; conse- 

 quently when great size of pinion is attained, as in 

 butterflies and moths, without efficient working 

 machinery, weakness and sluggishness supervene. 

 On the other hand, when wing, weight, and working 

 power are accurately balanced, as in the dragon-fly, 

 no bird can outstrip it. 



Finally, despite the excellence of the bird machinery 

 generally, few are perfect flying machines. As in 

 insects, infinite grades of motor mechanism abound, 

 showing infinite varieties of sketch models, from the 

 eagle to the dodo, while monstrosities are not un- 

 common. The ostrich's wings, for instance, only 

 assist it in running; and the penguin's for paddling 

 in the water or scudding over its surface. Barn fowls 

 are not particularly aerial, while the arctic auk, the 

 garfou, and the puffin are mere caricatures of birds. 

 Indeed, when we consider that no less than 5000 

 species of birds are known, each with its own special 



