in] THE FACTORS OF DISTRIBUTION 71 



tissue waste is reduced to the minimum ; and the 

 animal hibernates by burying itself in the sand at the 

 sea-bottom. The tissues are however wasted away 

 to a greater extent than they are renewed, and the 

 ' condition ' of the fish is at its worst at the period of 

 minimal sea temperature. 



The rate of development of the embryo of a 

 marine animal varies also with the temperature ; 

 thus a flounder embryo will hatch out from the egg 

 in about ten days at the beginning of the spawning 

 period, when the water is coldest ; but it will hatch 

 out in about six days at the end of the spawning 

 period when the water has become much warmer. 

 This relation holds for all developing eggs of cold- 

 blooded animals which have been investigated, and 

 it has been stated as follows ; for a difference of 

 temperature of 10 C. 



Average duration of development at nC. _ 2 '85 

 Average duration of development at (n 10) 1 



which means that when the temperature is reduced 

 by 10C. the time required for the hatching out of 

 the embryo of a marine animal is increased about 

 threefold. 



The duration of life also varies with the tempera- 

 ture in such a way that the lower the temperature of 

 its life-medium the longer an animal lives. Probably 

 this also holds good for warm-blooded animals for 



