2SO PHYSIOLOGY OF THE INVERTEBRATA. 



builders either do not secrete carbonate of lime in their body- 

 walls, or, if they do so, the skeletons are much less massive 

 than in tropical waters." No doubt this difference in the 

 function of lime-secreting is partly due to the direct action 

 of the environment, and partly to natural selection. Mr. 

 Herbert Spencer, in his Prind'pUs of Biology^ has pointed 

 out the influence of the environment on the simplest uni- 

 cellular organisms, tracing it up to more and more complex 

 organisms, and he has further shown its struggle with 

 atavism, or the principle of heredity, so strongly possessed 

 by all animal and vegetal cells. There is every reason to 

 believe that the direct action of the environment has in- 

 fluenced the protoplasm of the representatives of the coral- 

 polyps living in cold seas, so that it no longer possesses the 

 same power of secreting carbonate of lime. 



(i) " In descending into deep water in equatorial regions, 

 the amount of carbonate of lime secreted by the animals 

 living on the sea bottom becomes less with increasing 

 deptii." 



(c) " The number of species and individuals of lime- 

 secreting organisms decreases " with the distance from the 

 equator. It appears that these organisms " secrete more 

 lime in regions where there is a unifoi'uily high temperature 

 of the ocean water than in those regions Avhere there are 

 great seasonal fluctuations of temperature, or where there is 

 a uniformly low temperature of the water, as in the polar 

 regions and in the deep sea." 



{(I) " In temperate seas more carbonate of lime is secreted 

 in the warm summer months than during the winter months. 

 Indeed, a high temperature of the sea water is more favour- 

 able to abundant secretion of carbonate of lime than high 

 salinity." 



(<') " The average percentage of carbonate of lime in the 

 vlwU of til r dqwsits covering the floor of the ocean is 36*83, 

 and of this carbonate of lime, it is estimated that fully 90 

 per cent, is derived from the remains of pelagic organisms 



