Ill] OF TURGESCENCE 245 



another. It has an upper limit of size vaguely characteristic of the 

 species, and if fed well and often it may reach it in a year ; on stinted 

 diet it grows slowly or may dwindle down; it may be kept at 

 wellnigh what size one pleases. Certain full-grown anemones were 

 left untended in war-time, unfed and in water which evaporated 

 down to half its bulk; they shrank down to little beads, and grew 

 up again when fed and cared for. 



Loeb shewed, in certain zoophytes, that not only must the cells 

 be turgescent in order to grow, but that this turgescence is possible 

 only so long as the salt-water in which the cells lie does not overstep 

 a certain limit of concentration: a limit reached, in the case of 

 Tubularia, when the salinity amounts to about 3-4 per cent. Sea- 

 water contains some 3-0 to 3-5 per cent, of salts in the open sea, 

 but the salinity falls much below this normal, to about 2-2 per cent., 

 before Tubularia exhibits its full turgescence and maximal growth; 

 a further dilution is deleterious to the animal. It is likely enough 

 that osmotic conditions control, after this fashion, the distribution 

 and local abundance of many zoophytes. Loeb has also shewn* 

 that in certain fish-eggs (e.g. of Fundulus) an increasing concentration, 

 leading to a lessening water-content of the egg, retards the rate of 

 segmentation and at last arrests it, though nuclear division goes on 

 for some time longer. 



The eggs of many insects absorb water in large quantities, even 

 doubling their weight thereby, and fail to develop if drought prevents 

 their doing so ; and sometimes the egg has a thin- walled stalk, or else 

 a "hydropyle," or other structure by which the water is taken inf. 



In the frog, according to Bialaszewicz J, the growth of the embryo 

 while within the vitelline membrane depends wholly on absorption 

 of water. The rate varies with the temperature, but the amount 

 of water absorbed is constant, whether growth be fast or slow. 

 Moreover, the successive changes of form correspond to definite 

 quantities of water absorbed, much of which water is intracellular. 

 The solid residue, as Davenport Has also shewn, may even diminish 



* P finger's Archiv, lv, 1893. 



t Cf. V. B. Wigglesworth, hised Physiology, 1939, p. 2. 



% Beitrage zur Kenntniss d. Wachstumsvorgange bei Amphibienerabryonen, Bull. 

 Acad. Sci. de Cracovie, 1908, p. 783; also A. Drzwina and C. Bohn, De Taction. . .dea 

 solutions salines sur les larves des batraciens, ibuL 1906. 



