126 THE RATE OF GROWTH [ch. 



vitelline membrane depends wholly on the absorption of water ; 

 that whether rate of growth be fast or slow (in accordance with 

 temperature) the quantity of water absorbed is constant; and 

 that successive changes of form correspond to definite quantities 

 of water absorbed. The solid residue, as Davenport has also 

 shewn, may actually and notably diminish, while the embryo 

 organism is increasing rapidly in bulk and weight. 



On the other hand, in later stages and especially in the higher 

 animals, the percentage of water tends to diminish. This has 

 been shewn by Davenport in the frog, by Potts in the chick, and 

 particularly by Fehhng in the case of man*. Fehhng's results 

 are epitomised as follows : 



Age in weeks ... 6 17 22 24 26 30 35 39 

 Percentage of water 97-5 91-8 92-0 89-9 86-4 83-7 82-9 74-2 



And the following illustrate Davenport's results for the frog: 



To such phenomena of osmotic balance as the above, or in other 

 words to the dependence of growth on the uptake of water, Hober f 

 and also Loeb are inclined to refer the modifications of form 

 which certain phyllopod Crustacea undergo, when the highly 

 saline waters which they inhabit are further concentrated, or are 

 abnormally diluted. Their growth, according to Schmankewitsch, 

 is retarded by increase of concentration, so that the individuals 

 from the more saline waters appear stunted and dwarfish; and 

 they become altered or transformed in other ways, which for the 

 most part suggest "degeneration," or a failure to attain full and 

 perfect development J. Important physiological changes also 

 ensue. The rate of multiplication is increased, and partheno- 

 genetic reproduction is encouraged. Male individuals become 

 plentiful in the less sahne waters, and here the females bring forth 



* Febling, H., Arch, fiir Gynaekologie, xi. 1877; cf. Morgan, Experimental 

 Zoology, p. 240, 1907. 



t Hober, R., Bedeutung der Theorie der Losungen fiir Physiologie und 

 Medizin, Biol. Centralhl. xix, 1899; cf. pp. 272-274. 



t Schmankewitsch has made other interesting observations on change of size 

 and form, after some generations, in relation to change of density; e.g. in the 

 flagellate infusorian Anisonema acinus, Biitschli {Z. /. w. Z. xxix, p. 429, 1877). 



