84 Causes of Emigrations 



in thermal waters, which renders respiration more difficult for 

 purely aquatic animals" (Brues, 1927) . Most of the inhabitants 

 of hot springs are air breathers. The rat-tailed maggot (Eristalis) , 

 for example, is quite characteristic. Its jointed, telescoping breath- 

 ing tube reaches to the surface and permits the inspiration of air. 



There are two types of animals which have left the ocean on 

 account of temperature influences. Some euryhalin animals like 

 the salmon, ciscoes, and certain crustacean relicts, which spawn on 

 the pebbly bottoms near the headwaters of streams (Chidester, 

 (1924) or now live permanently in the cool, profundal regions of 

 deep lakes, are little limited in their environmental relations by 

 variations in salinity but are associated primarily with cold water. 

 These animals have spread from the ocean whenever there was 

 opportunity. A nice illustration of the dependence of ciscoes on 

 low temperatures is given by Fry (1937). In Lake Nipissing they 

 move from shallow to deep water in summer and remain until lack 

 of oxygen forces them near or above the thermocline. They feed 

 less and grow less in deep water. The other type of animals has 

 left the ocean, invaded fresh water, and then been forced to take 

 up life on land in the tropics, where high temperatures make 

 metabolism of poikilothermic animals rapid and thus increase 

 oxygen requirements where the oxygen content of the water is 

 often low and the atmosphere often humid. This combination of 

 factors makes respiration in shallow fresh waters difficult and 

 permits life on land without great danger of desiccation and loss 

 of activity on account of low temperatures. 



Adaptations which enable animals to live on land at low or 

 high temperatures may be concerned with bodily temperature 

 regulation, the prevention of water loss, water storage, or the 

 assumption of torpid states. Hibernating insects are prepared 

 for low temperatures by the increase in bound water in their bodies 

 (Robinson, 1928), or, what perhaps amounts to the same thing, 

 a decrease in free water (Bodine, 1923). Mammals also prepare 



