DESIGN IN THE ORGANIC WORLD. 441 



that it can be so transformed. The existence of the "potentiality," 

 and of the wonderful instinct that leads the worker bees to act 

 upon it, are not less evidences of "design," because physical 

 agencies are needed to call them into exercise. 



A familiar instance of adaptiveness between the conformation 

 of animals and their environment, is the possession by Birds and 

 Mammals inhabiting the Polar regions, of a tegumentary covering 

 that serves to keep in the warmth of their bodies, the former 

 being provided with an underclothing of down, the latter with a 

 thick close fur ; whilst, on the contrary, many of the larger 

 quadrupeds inhabiting the torrid zone show a marked deficiency, 

 or even entire absence, of hairy covering. Now this is the more 

 remarkable, because the ordinary effect of external warmth is to 

 increase, and of external cold to diminish, the determination of 

 blood to the skin ; of which we see the effects alike in the increase 

 of perspiration, and in the more rapid growth of the hair and nails 

 during summer. Yet I have myself seen in Southdown sheep, 

 which had been transported only two years previously to the 

 West Indies, the thick covering of wool replaced by short crisp 

 hair, scarcely distinguishable from that of the goats which had 

 inhabited the island for several generations ; and the hottest parts 

 of the South American Pampas are inhabited by breeds of cattle 

 (the descendants of those introduced by the Spaniards), of which 

 some are nearly, and others quite, destitute of hair, and which 

 cannot live in the more temperate air of the slopes of the 

 Andes. It seems clear, then, that this adaptation results from 

 some direct physical action of temperature on the constitution 

 of the animals ; and yet (like the expansion of water in cooling 

 from 392° to 32°) it is in direct opposition to a very general 

 law. 



The same may be said of the winter whitening of the fur and 

 plumage of Arctic Mammals and Birds. For although this (like 

 the preceding) has been adduced as an example of "natural 

 selection, " — the white varieties surviving because they escape 

 being seen upon ground whitened by snow, — yet there must have 

 been some cause for the production of the white varieties ; and 

 it has been the experience of some of our Arctic voyagers, 

 that the winter whitening could be retarded by keeping the 



