Osviotic Eqwilihration. 235 



We thus see that in the evolution of the race there has been 

 a steady growth of the tendency of the individual to become 

 independent of its environment (and therefore not compelled 1o 

 change in response to alterations in that environment) by means 

 of maintaining through the co-ordinated and integrative action 

 of all its organs, constancy in the action of its vital parts. 



The removal of its vital organs from the disturbances of func- 

 tion which must of necessity folloAv alterations in the physical 

 and chemical properties of their environment, which in the 

 higher animals are dependent on those of the circulating fluid, 

 was the first great advance, and ensured for the organism the 

 better and more efficient action of these organs, and afforded 

 a distinct impetus to higher specialisation and greater independ- 

 ence of externa] environmeiitHl change. Thus, tlie beginning of 

 the development of the firm resistant bony skeleton in place of 

 the soft cartilaginous framework, and the formation of a high 

 type of tissue from a simple one which this advance implies, 

 most probably began to take place at a time in the history 

 of the race when the cartilaginous fish was leaving the sea and 

 taking to the mud of estuaries, where it most probably also 

 developed the mechanism for maintaining the salt ratios and 

 osmotic pressure of its blood a constant. 



The sea water which is contained in the oceans of the present 

 day gives a A of about 2.30C. Bottazzi (1) gives a long series 

 of determinations of the A of the body-fluids of many marine 

 forms, and his results show that this A is approximately that 

 of the sea-water environment in the case of coelenterates, echino- 

 derms, crustaceans, gastropods, cephalopods amongst the inver- 

 tebrates, and the elasmobranch fishes amongst the vertebrates. 



Then there is a jump, and the blood of teleosts is found to 

 give a A of about 1, and my own observations on the blood of 

 the barracouta, a teleost inhabiting Australian waters, confirms 

 these results. (A of water of Hobson's Bay about 2.1.) The 

 next sea animals that we come to are the sea turtles, with a A 

 of 0.7, and the next the sea mammals — seals, dolphins and 

 whales. The determinations of the A of the blood of these 

 animals have been made by Portier (11), Rodier (12), and Jolyet 

 (5), on the blood of animals Avhich had been recently killed. 

 Post-mortem decomposition may explain to a small degree the 



