158 THE OCEAN 



birds — ^like the penguins — are to be regarded 

 as marine creatures, then they have a still 

 higher blood-temperature, which remains prac- 

 tically constant although the external condi- 

 tions vary greatly. 



The vast majority of marine animals belong 

 to the second group, in which the blood-tem- 

 perature is the same as that of the surrounding 

 water or a very little higher. This group 

 includes the fishes and all invertebrates. In 

 the tunny-fish the temperature of the blood 

 was observed to be sometimes as much as 6° F. 

 above that of the surrounding water, but this 

 was after great exertion and is exceptional. 

 There are in the polar regions many species, 

 belonging to nearly all the marine groups, 

 which pass the whole of their lives in water 

 having a temperature below the freezing 

 point of fresh water. In the tropics, however, 

 animals belonging to the same groups, star- 

 fishes for example, pass the whole of their 

 existence in water having a temperature of 

 about 80° F. It is well known that chemical 

 reactions are so influenced by temperature that 

 the velocity of a reaction is doubled or trebled 

 when the temperature is increased by 18° F. 

 This is known as van t'Hoff's law, and is 

 strictly applicable to biochemical reactions 

 in plants. The evidence available shows 

 that the same may be inferred with regard to 



