PACKARD.] TEANSFOEMATION OF ARTEMIA. 471 



summer of 1870, tlien not yet being aware that, aeconling to Professor 

 Siebold's investigations, no males conld be developed.^ The same error 

 crept into an extract of the protocol, sessions of tlic zoological part of the 

 third meeting of Eussian naturalists at Kiew contained in this journal 

 (Zeitsch. f. w. Zoologie), and this gave Professor von Siebold occasion for 

 a timely remark.' Taking advantage of the present occasion to correct 

 the mistake, observing that it was not printed in my paper, although 

 the latter, together with the report, was prepared in the same session, 

 I have yet to add that Artemia salina becomes accustomed to gradual 

 changes in the concentration of salt water in the lake, as well as in do- 

 mesticating them, and then becomes fitted to stand a very high or very 

 low density of the water, so that either of them form a suitable envi- 

 ronment. In rapidly changing the concentration of the salt water the 

 same is rendered unfit to sustnin life, changing the manner of obtaining 

 food, and produces, at the same time, in a state of nature, the ai)pear- 

 ance of males in forms to "which ])arthenogen(?sis is peculiar. 



I had already observed this in Artemia in the lake, but saw this es- 

 pecially in Daplmia with artificial domestication of non-isolated females, 

 that the males of the domesticated S])ecies first appear on the most ex- 

 treme life-sustainable limits of the surrounding elements, i. e., as well 

 at a too low as at a too high temperature. 



If we domesticate the fresh- water species, Baphnia magna Leydig, in 

 weak salt water, which they stand well, there appear, at this compara- 

 tively rapid heightening of density of the salt water, males and fertil- 

 ized eggs at such a moderate temperature, at which ordinarily the same 

 species in fresh water propagates })arthenogenetically. 



In the Hadschibei Lake occurs Daplmia rectirostris Leydig, at a den- 

 sity of the salt water of 5° to 8° B., especially in spring and fall ; the 

 same disappearing in summer at a higher density of the salt lake, 

 while befoie the females often in the middle of the summer cease to pro- 

 pagate parthenogenetically, bearing as in fall fecundated eggs in 

 ephippia. 



Altogether I i)roduced during the artificial domestication of Daphuia 

 the appearance of males and fecundated eggs through rapid augmenta- 

 tion of the density of the salt water as well as through rapid increase of 

 temperature. However it is difficult to say which will be the mean of 

 concentration for a known species of Artemia, because a slightly less- 

 ened density, though favorable for the growth of the individual, weakens 

 its ])ower of propagation, while a heightened density augments (or sup- 

 ports) propagation, on the other hand this being a hindrance for the 

 development of the individuals. The undiscovered mean of density, it 

 seenis to me, must be between these two i)oints, the most extreme limits 

 of the favorable condition of the surrounding elements being then out- 

 side of those two points. 



On these lijnits we must find a density at which the males appear in 

 the lake in great multitudes, as several observations and analogous in- 

 vestigations on Daphnia have demonstrated. 



1 therefore recede from my opinion that the males of Artemia appear 

 at a mean densitj' of the salt Avater, if the mean density is determined 

 between that of favoring the development and that of assisting the pro- 

 pagation. 



Until now I have found the greatest number of males o£ Artemia sa- 

 lina in the Hadschibei Lake in the middle of the summer of 1870, at a 



^C. von Siebold, Reitriige znr Partlienogenesis der Artbropodeu. 1871, p. 224. 



2 0. von Siebold, Ueber Partlienogenesis der Art. salina. Extract of the sessions of 

 th,e Koyal Academy of Sciences at Miinchen, Itil'S, p. 190. 



