474 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



For the purpose of illustrating this, 1 havecliosen Baphnia rectirostris 

 Leydiji' {Bloina rectirostris Baird) aud Branchipus ferox Cbyzer. 



Baphnia rectirostris occurs here in large numbers in fresh-water basins, 

 brine ditches, and also in the Chadschibaisky Salt Lake. In the latter 

 they occurred at a concentration of from five to eight degrees of 

 Beaume's areometer. Two characters are seen in the Baplinia rectiros- 

 tris living in so diversified elements, the former dej)cnding on the latter. 

 It appears firstly, that in salt water, and especially in the more saline 

 Chadschibai Lake the middle temperature is lower, i. e.. the temperature 

 more favorable for the life of Baphnia rectirostris than the temi)erature 

 favoring the life of the same Daphuia in fresh water, so that the Daph- 

 nia, being in reality a summer form of the fresh waters, changes in salt 

 water into a fall form, occurring till the beginning of winter in the salt 

 lake at a concentration of 7° to S^' Beaume in immense quantities, even 

 remaining viviparous at a temperature at which the individuals of the 

 fresh-water generations of the same species could live no longer. Sec- 

 ondly, the individuals of the salt-lake generations of Baphnia rectirostris 

 represent a degraded or retrograde form of the fresh -water generations 

 of the same species, differing from the latter the more the higher the 

 concentration of the salt-w^ater basins in which they occur increases, 

 so that the individuals of the salt lake differ more from the fresh- water 

 forms than the individuals living in salt ditches. 



So much do the forms of Baphnia rectirostris from the salt lake differ 

 from those of the fresh waters that they could be regarded as a separate 

 variety of Baphnia rectirostris, although it is but a transformed gener- 

 ation letarded in its development, and changed under the influence of 

 the surroundings of Baphnia rectirostris inhabiting the fresh waters. 

 On account of various observations and experiments, I presume that 

 the peculiarities of the salt-lake form of Baphnia rectirostris are entirely 

 dependent on the properties of the salt water which they inhabit. 



Baphnia rectirostris cannot stand in summer a density of the water 

 of the salt lake of iP B., while it lives in great quantities in the same 

 salt lake at a density of 8° B. in the fall, toward the end of October 

 and in November, being than vivii)ai'ous, that is, at such a season in 

 which the fresh-water form of our Daphnia has. already ceased to live. 

 Tills is not an extraordinary phenomenon, considering that a certain 

 aeration of the water is unconditionally necessary to sustain the life of 

 Baphnia rectirostris, and that it is unimportant by which means the 

 aeration of the w^ater is regulated. Agreeing w4th the physical law 

 the less the aeration of the salt water, the higher its density becomes, 

 which results that fresh water must contain more air than any salt 

 water of the same temperature. It consequently follows that also in 

 a salt water of certain concentration at a corresponding low^er tem- 

 perature the same quantity of air as in fresh water could be contained. 

 It is obvious that the quantity of air in the water of the Chadschibai 

 Lake toward the end of October and at a density of 8° B. could approxi- 

 mately be the same as that in fresh water during tlie summer, and 

 therefore the processes of nutrition in the organism of Baphnia rectiros- 

 tris could in reality be as favorable in both the fresh and salt water. 

 Tliough analogous in general, they differ singly from each other, as, for 

 instance, by the higher pressure of the more dense water, which density 

 again depends on the quantity of salt aud the lower teuiperature of the 

 water. Dej^endant on such differences between salt and fresh w^ater 

 are also partly some differences in the organization of the salt and fresh 

 water forms of Baphnia rectirostris. 



In the females of the Chadschibai Lake, the penicilii or fascicles of 



