NATUEAL HISTOHY OF LAKE UBMI. 359 



an abundant crop of literature dealing with the effect of 

 salinity upon the early stages in the development of organisms 

 and especially of Echinoderms (Morgao, Loeb, Eawitz, Norman, 

 Vernon, and other students of " Entwickelungsmechanik "). 

 None, however, are of more importance than the classical 

 treatises of Schnankewitsch upon BrancMpns, Artemia salina, 

 and A. Mulhausenn. By some accident a tank near Odessa 

 became filled witli salt water of a density of 1-0567 (8° Beaume) 

 in 1871. The water in the tank became concentrated by very 

 gradual evaporation until in 1874 it reached a density of 1*2015 

 (25° B.). The Artemia salina which populated the tank in 

 1871 underwent a gradual change as the salt water became 

 more and more concentrated. The setae of the fureal lobes of 

 the tail became fewer in number and dwindled in size, the gill- 

 lamellge enlarged and altered in shape, the abdomen tended 

 to alter its segmentation, and finally the entire species became 

 metamorphosed im o A. Mulhausenii, a species only known from 

 the most saline wat'-rs. 



The Artemia nrminna lives in a far more saline water than 

 the A. salina of Schmankewitsch did, but not in such a saline 

 solution as A. Mulhausenii. Consequently we should expect 

 A.urmianato be in ermediate in structure between these forms in 

 those characters w ich are determined by the strength of the saline 

 environment ; and this is precisely what I have found to be the 

 case with respect to the tail-lobes and their setae. Many of the 

 Artemia urmiana e \hibit clearly the intermediate condition fio-ured 

 by Schmankewitsch on plate vi. fig. 5* The specific gravity of 

 the water which produced this condition in Schmankewitsch's 

 experiment was about 1-1373, while the specific gravity of the 

 water of Lake Urmi is 1*1138, or '0235 lower. It must be remem- 

 bered that the salinity in the ponds of Schmankewitsch was 

 increasing at a very rapid rate as compared with the rate of 

 change of the salinity of Lake Urmi. It is therefore likely that 

 if the Artemias of Odessa had had more time, as measured by 

 Artemia-gen.^ra,i\on», in which to adapt their structure to a salinity 

 indicated by a specific gravity of 1-1138, the resemblance between 

 the Hussian and Persian Artemias would have been even yefc 

 more striking. Even as it is, the Artemia seems to act as a 

 hydrometer with an error of less than 'OS in the determination 

 of specific gravities. 



* Zeitschr. f. wiss. Zool. 1875. 



