Acclimatization 139 



variations in temperature, salinity, and other factors which accom- 

 pany landward migrations. Starfish larvae do not have much ability 

 to adjust themselves to higher temperatures, but ciliates do (Jacobs, 

 1919). A fish consumes three times as much food at 20 C. as at 

 10°C. (Hathaway, 1927). Animals can, if subjected to altered 

 environmental conditions, alter their range of activities to some ex- 

 tent, i.e., they become acclimatized to new levels (Davenport, 1908; 

 Huntsman, 1924a, 1924b; Compel & Legendre, 1927). As time for 

 its metamorphosis approaches, a toad tadpole loses much of its 

 ability to endure high temperatures (Hathaway, 1928) . As it pre- 

 pares for land life, it acquires new powers and loses old abilities. 

 Adjustments usually involve such compensations in the way of 

 acquisitions and losses. 



Acclimatizations often result in rhythmical adjustments to regu- 

 larly recurring variations in environment. As such variations are 

 more extreme in land and fresh-water habitats than in the sea, ani- 

 mals in the former generally show more striking adjustments than 

 those in the latter. The differences between the habits of nocturnal 

 and diurnal animals, for example, are on the whole greater among 

 land animals than among those in the ocean. When the environ- 

 ment is most variable, ranges of physiological endurance and ad- 

 justment are usually wider. Under such circumstances it is not 

 strange that homoiothermic animals, while they enjoy the stimulat- 

 ing uncertainty of life on land, have attained some degree of stabil- 

 ity by having constancy in internal fluids which bathe living cells 

 and in body temperatures. 



Kennedy (1925) has "come across two species of insects, one a 

 dragonfly, the other a mayfly, in which a reversal of one or more of 

 the tropisms normal to the other species of the same genus has per- 

 mitted the entrance of these reversal species into environments not 

 open to normal members of the genus." These insects have made 

 adjustments which have given them special advantages by forsaking 

 traditional modes of behavior for their types. 



