254 THE RATE OF GROWTH [ch. 



for instance, contain large quantities of magnesium sulphate; and 

 the Artemiae continue to live equally well in artificial solutions 

 where this salt, or where calcium chloride, has largely replaced the 

 common salt of the more usual habitat. Moreover, such waters as 

 those of the natron-lakes are subject to great changes of chemical 

 composition as evaporation and concentration proceed, owing to the 

 different solubilities of the constituent salts; but it appears that 

 the forms which the Artemiae assume, and the changes which they 

 undergo, are identical, or indistinguishable, whichever of the above 

 salts happen to exist or to predominate in their saline habitat. At 

 the same time we still lack, so far as I know, the simple but crucial 

 experiments which shall tell us whether, in solutions of different 

 chemical composition, it is at equal densities, or at isotonic concen- 

 trations (that is to say, under conditions where the osmotic pressure, 

 and consequently the rate of diffusion, is identical), that the same 

 changes of form and structure are produced and corresponding 

 phases of equihbrium attained. 



Sea-water has been described as an instance of the "fitness of the 

 environment*" for the maintenance of protoplasm in an appropriate 

 milieu; but our Artemias suffice to shew how nature, when hard 

 put to it, makes shift with an environment which is wholly abnormal 

 and anything but "fit." 



While Hober and others f have referred all these phenomena to 

 osmosis, Abonyi is inclined to believe that the viscosity, or 

 mechanical resistance, of the fluid also reacts upon the organism; 

 and other possible modes of operation have been suggested. But 

 we may take it for certain that the phenomenon as a whole is not 

 a simple one. We should have to look far in organic nature for 

 what the physicist would call simple osmosis % ; and assuredly there 

 is always at work, besides the passive phenomena of intermolecular 



* L. H. Henderson, The Fitness of the Environment, 1913. 



t Cf. Schmankewitsch, Z. f. w. Zool. xxv, ISTi); xxix, 1877,. etc.; transl. in 

 appendix to Packard's Monogr. of N. American Phyllopoda, 1^83, pp. 466-514; 

 Daday de Dees, Ann. Sci. Nat. (Zool), (9), xi, 1910; Samter und Heymons, Abh. 

 d. K. pr. Akad. Wiss. 1902; Bateson, Mat. for the Study of Variation, 1894, pp. 

 96-101; Anikin, Mitlh. Kais. Univ. Tomsk, xiv: Zool. Centralhl. vi, pp. 756-760, 

 1908; Abonyi, Z.f. w. Zool. cxiv, pp. 96-168, 1915 (with copious bibliography), etc. 



% Cf. C. F. A. Pantin, Body fluids in animals, Biol. Reviews, \i, p. 4, 1931; 

 J. Duclaux, Chimie apjMquee a la biologic, 1937, ii, chap. 4. 



