272 THE EFFECT OF MOISTURE 



The history of these observations is as follows: 

 Through the breaking of a dam across a salt lake 

 (Kuyalink), a number of individuals of A. salina were 

 washed from the upper less saline waters into the lower 

 more concentrated waters, and the Specific Gravity of 

 these was at the same time reduced to 1.058. After 

 the dam was repaired the concentration gradually in- 

 creased again through evaporation, the Specific Gravity 

 rising to 1.105 the year after; to 1.135 the next year, 

 and to 1.205 the year after that. Accompanying this 

 concentration, the generations of Artemia progressively 

 degenerated, till they finally attained the characters of 

 A. milhausenii. Schmankewitsch also succeeded in con- 

 verting a brood of A. salina into A. milhausenii by the 

 artificial process of gradually increasing the percentage 

 of salt in the water in which they were living (the 

 Specific Gravity being raised from 1.028 to 1.205). 



These two forms of Artemia have been held to be 

 distinct species, in that milhausenii shows an absence of 

 fins and bristles on the lobes of the tail, and has much 

 smaller tail lobes, but larger branchial appendages to 

 the legs, than salina. Schmankewitsch himself did not 

 hold this opinion, however, and Bateson,* who has 

 recently studied the question afresh, thinks similarly. 

 Bateson collected samples of Artemia from a number of 

 different salt lakes in Western Central Asia and West- 

 ern Siberia, and, consonant with Schmankewitsch's 

 statement, he found that, on the whole, the number of 

 bristles on the caudal fins, and likewise the size of the 

 fins, was smallest in specimens collected from waters of 

 high Specific Gravity. The accompanying table shows 

 * " Materials for the Study of Variation," p. 96. 



