THE LIVING WORLD 249 



ermine and the Arctic fox become white in winter and 

 so match with the snow. 



Sometimes creatures will change colour readily, as is 

 the case with the chameleon and some insects ] modifica- 

 tions of form and colour often attend the advent of the 



FIG. 53. 



TWO PLANTS, VERY DIFFERENT IN NATURE, WHICH GREATLY 

 RESEMBLE EACH OTHER EXTERNALLY. 



A A cactus (Cereus) from Brazil. 



B A spurge (Euphorbia) from Africa. 



breeding season, with vocal manifestations, such as of 

 singing birds, croaking frogs, and rutting stags. 



The environment of organisms will also affect them in 

 many other ways, besides their colours. Thus the use 

 of soft food seems to have diminished the jaws of both 

 civilised men and their pet dogs. English oysters 

 transported to the Mediterranean are said to alter 

 their mode of growth rapidly, so as to resemble the 



