144 REPRODUCTION IN PLANTS AND ANIMALS. 



re-clothed. It is the season of love and happiness. All 

 nature rejoices. To many organized beings it comes only 

 once. In this respect many animals are like annual plants, 

 perishing as soon as they have given birth to their eggs. 

 The lives of insects especially are thus limited. 



The cause of this grand revolution of the exterior of 

 organized beings, results from the antecedent restraint of 

 their functions by the cold of winter. The vital properties 

 of the tissues of animals and plants are still retained, 

 although neither may exhibit any outward indications of 

 life. As the temperature of the air declines to the freezing- 

 point, the movements of life either cease altogether or 

 become quite imperceptible ; but when the temperature 

 again rises, the usual activity of the plant and animal 

 returns. 



There are different degrees of torpidity in both animals 

 and plants. Some animals retire into situations favorable 

 to the retention of their warmth, and occasionally awaken 

 in mild weather and apply themselves to the store of food 

 which they have previously accumulated in autumn. In 

 other species, there is an accumulation of fat in the body 

 of the animal which keeps up its temperature above that of 

 the surrounding air. These animals may be roused from 

 their torpidity into which they soon fall again ; their re- 

 spiratory movements, though diminished in frequency, are 

 still continued. But in the Marmot and other animals 

 which hibernate completely, the heat of the body almost 

 entirely accords with that of the surrounding air, being 

 seldom more than one or two degrees higher. The respi- 

 ratory movements fall from 500 to 14 per hour, and the 

 pulse sinks from 150 to 15 beats per minute.* Thus the 



* See Carpenter. 



