Ill] OF OSMOTIC REGULATION 251 



merit*. Important physiological changes ensue. The consumption 

 of oxygen increases greatly in the stronger brines, as more and more 

 active " osmo-regulation " is required. The rate of multiplication is 

 increased, and parthenogenetic reproduction is encouraged. In the 

 less sahne waters male individuals, usually rare, become plentiful, 

 and here the females bring forth their young alive ; males disappear 

 altogether in the more concentrated brines, and then the females 

 lay eggs, which, however, only begin to develop when the sahnity 

 is somewhat reduced. 



The best-known case is the little brine-shrimp, Artemia salina, 

 found in one form or another all the world over, and first discovered 

 nearly two hundred years ago in the salt-pans at Lymington. 

 Among many allied forms, one, A. milhausenii, inhabits the natron- 

 lakes of Egypt and Arabia, where, under the name of "loul," or 

 "Fezzan-worm," it is eaten by the Arabsf. This fact is interesting, 

 because it indicates (and investigation has apparently confirmed) 

 that the tissues of the creature are not impregnated with salt, as 

 is the medium in which it hves. In short Artemia, hke teleostean 

 fishes in the sea, hves constantly in a "hypertonic medium"; the 

 fluids of the body, the milieu interne, are no more salt than are those 

 of any ordinary crustacean or other animal, but contain only some 

 0-8 per cent, of NaCl J , while the milieu externe may contain from 

 3 to 30 per cent, of this and other salts; the skin, or body- wall, of. 

 the creature acts as a "semi-permeable membrane," through which 

 the dissolved salts are not permitted to diffuse, though water passes 

 freely. When brought into a lower concentration the animal may 

 grow large and turgescent, until a statical equilibrium, or steady 

 state, is at length attained. 



Among the structural changes which result from increased con- 



* Schmankewitsch, Zeitschr. f. wiss. Zool. xxix, p. 429, 1877. Schraankewitsch 

 has made equally interesting observations on change of size and form in other 

 organisms, after some generations in a milieu of altered density ; e.g. in the flagellate 

 infusorian Ascinonema acinus Biitschli. 



t These "Fezzan- worms," when first described, were supposed to be "insects' 

 eggs"; cf. Humboldt^ Personal Narrative, vi, i, 8, note; Kirby and Spence, Letter x. 



X See D. J. Kuenen, Notes, systematic and physiological, on Artemia, Arch. 

 N4erland. Zool. iii, pp. 365-449, 1939; cf. also Abonyi, Z.f. w. Z. cxiv, p. 134, 1915. 

 Cf. Mme. Medwedewa, Ueber den osmotischen Druck der Haemolymph v. Artemia; 

 in Ztsch. f. vergl. Physiolog. v, pp. 547-554, 1922. 



