HIBERNATION. 23 



mammals, digestion and respiration being entirely suspended. 



Frogs generally hibernate in masses in the mud in the 

 bottom of the water, and if awakened from this state by 

 warmth can remain under water without drowning eight times 

 longer than frogs in the mating season. The toad appropri- 

 ates some cosy burrow in the ground, where he defies the 

 freezing weather. 



Hibernation has been observed in man}^ of the fishes of the 

 temperate zones. Fishes do not fall into a condition of com- 

 plete torpidity, as do reptiles and mammals, but their vital 

 functions are simply lowered, and they hide in sheltered holes 

 and cease to go abroad in search of food. It is stated that in 

 India, where ponds may become dry at certain seasons for the 

 depth of many feet, fish which have been imprisoned for sev- 

 eral years in hardened mud have assumed their wonted activ- 

 ity when released from their uncomfortable position by copious 

 rains. 



When the temperature of water reaches the freezing point 

 yellow perch become torpid, but above 38 or 40 degrees they 

 suffer no inconvenience. Black bass do not seem to closely 

 depend on temperature. Having no opportunit}' of escaping 

 the cold they sink to the deepest part of their wateiy domain 

 at the approach of Winter and if the chill penetrates to their 

 retreat their vitality is diminished, their blood flows more 

 slowly, they feel no need of food, and forthwith enter into 

 hibernation. A gentleman kept a bass in his aquarium nearly 

 all of one Winter. It ate nothing and seldom moved any 

 member except its eyes. 



The eel generally retires to the sea in Winter, but where 

 migration is impossilDle it avoids the cold by burrowing in the 

 mud. In these situations it has been captured by spearing 

 through holes cut in the ice. 



Many species of mollusks hibernate. The land snails bury 

 themselves in the ground or conceal themselves under the bark 

 of trees, in holes in walls, or even in the stems of some plants. 

 They close the mouth of the shell with a calcareous plate, 



