242 J. L. Jona: 



environment would tend to produce, they have to a great degree 

 been able to withstand the accumulation of the toxic mag- 

 nesium in their body fluid. 



The postulation of an extra-marine ( iiuviatile ? ) existence 

 for the ancestors of the lobster (as advanced supra) would 

 account for this great difference l)etweeii limulus and the 

 lobster. 



We thus see that the animal economy at the elasmobranch 

 stage of its evolution is capable of resisting entry of toxic 

 chemical substances into its organisation, but not of withstand- 

 ing to any degree the physical forces of osmosis, so that, 

 although the animal's economy can to some degree determine 

 the salt ratios (and salt concentration too, as pointed out by 

 Bottazzi, 2), in its body-fluid, it is unable to resist the concentra- 

 tion of this fluid by the osmotic pressure exerted by the environ- 

 mental ocean. 



A table showing the genealogical relationships of the fishes 

 and higher vertebrates in accordance with the foregoino- con- 

 siderations and postulations is appended. (Appendix C.) 



My thanks are due to Professor W. A. Osborne, under whose 

 guidance this work was carried out. 



APPENDIX A. 



Osmotic Pressure of Liquid Foods. 



(Centigrade sc iJe em [ihii/ed throughout. J 



(Portions of the following results were published in the 

 Biochemical Journ., 1909.) 



Beverages. 



Coffee (2 tablespoonfuls of sugar in ordinary breakfast cup- 

 ful).— 



A 



(1) - - 0.341OC. 



(2) - - 0.343OC. 



Tea infusion {2 teaspoonfuls (about 12 c.c.) of tea leaves in 

 200 c.c, boiling water, allowed to infuse 5 minutes). — - 



