286 ELEMENTARY BIOLOGY 



calves, while others were fed on thyroid material. The former 

 lot of tadpoles grew to a large size, but remained tadpoles, 

 whereas the latter quickly passed through the stages of 

 development without increasing much in size (see Fig. 121). 

 333. Temperature and development. The temperature of 

 the water in which frogs' eggs are kept will influence the 



FIG. 122. Color changes in plumage 



The ptarmigan (Lagoptts lagopus) is snow-white in winter and replaces its coat with 



feathers containing more and more pigment as the seasons advance, reversing the process 



in the autumn, so that the plumage matches the surroundings the whole year round 



rate of development. The warmer it is, up to a certain point, 

 the more quickly will the tadpoles pass into the tailless stage. 

 Temperature may affect not only the rate of development 

 but other sides of the animal's make-up. Sheep taken to the 

 tropics lose their wool, and in New Guinea they become almost 

 bald. Some English dogs that had been taken to the higher 

 parts of the Himalayas developed a woolly coat. The hare, 

 like many other animals in temperate climates, has a summer 

 coat and a winter coat. In the Alps the animal carries its 

 winter coat about half the year ; in Norway, from eight to 

 nine months ; in Lapland, about ten months ; and in Greenland, 

 the whole year round. 



