AND OF SALINITY. 271 



but, after treatment with salted water (.3 to 1 per cent, 

 in strength), might contain a great deal. On the other 

 hand, watering cress with 1 per cent, solution caused 

 the starch normally present to disappear, either wholly 

 or in part. 



Upon the growth and even on the actual structure of 

 animals, changes of salinity may in some instances exert 

 a marked action. Animals accustomed to develop in 

 fresh water have their growth retarded by the addition 

 of salt. Thus Yung * reared frog's embryos in solu- 

 tions containing respectively 0, .2, .4, .6, and .8 per 

 cent, of salt, and found that except in the .2 per cent, 

 solution, which had no influence, there was a retarda- 

 tion in development. This increased with the concen- 

 tration of the solution, so that in the .8 per cent, solu- 

 tion the larvae took 17 days longer to hatch than in 

 pure water. Again, Sargeant t found that the rate of 

 reproduction by fission of the naid Dero vaga becomes 

 slower and slower according to the concentration of the 

 solution it is reared in. Taking the rate in pure water 

 as 11.3, it becomes reduced to 8.5 in .05 per cent, solu- 

 tion of salt, to 7.7 in .1 per cent, solution, 4.1 in .2 per 

 cent solution, and .3 in .3 per cent, solution. Still 

 stronger solutions stop reproduction altogether, and kill 

 off some of the worms. 



The more considerable effects which change of sa- 

 linity may produce are well illustrated by the interest- 

 ing and widely known observations of Schmanke- 

 witsch $ upon Artemia salina and A. milhausenii. 



*Arch. des Sci. Phys. et Nat., xiv. p. 502, 1885. 



f Davenport's " Experimental Morphology," p. 365. 



JZeit. f. wiss. Zool., xxv. p. 103, 1875, amZxxix. p. 429, 1877. 



