490 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



prosper in such non-diluted salt water, which was taken from the salt 

 lake at a middle concentration peculiar for this species {Artemia salina)^ 

 but thej^ do not prosper so well in a narrower jar with higher water-sur- 

 face, as they soon die in such a water. In the same narrow vessel and 

 at the same high water-level these animals will still ])rosper if the salt 

 water is i)roi)ortionally diluted. In this latter case the animals are so 

 circumstanced, as in more saline water in the broader jar with lower 

 water-level. The diluted water contains more air, it being more jjene- 

 trable and betler adapted for gas exchanges. 



5. Accepting the lact that the water in a salt lake at a given time 

 shows 10° Beaume, and that it is populated with crustaceans of the 

 genus Artemia, if we now take two equal vessels, placing in one of them 

 water of this salt lake and a certain number of specimens of one genus of 

 these crustaceans, and ])lacing in the other jar specimens of the same 

 animals out of the same salt lake, diluting the salt water to 1° or (P 

 Beaum6, a large number of animals will die in the first vessel under 

 the same conditions, while keeping up the initial concentration of tlie 

 water, but in tlie second vessel the majority of the animals will remain 

 alive. In tlie second case, that quantity of air is as if restored, which 

 is wanting in the first, apparently by the influence of the vessel itself, 

 as the water in the vessel is under different conditions from that iu the 

 salt lake. This is all the more so the case with a summer-like temj)era- 

 ture. 



6. The animals prosper also in a non-diluted salt water better at a 

 temperature lowered to a certain degree than at a higher temperature, 

 yet they do much better in diluted salt water, when the concentration 

 of the salt water has not been reduced above a certain degree. 



7. Finally, the enlargement of the surface of the gill-sacs in Artemia 

 with the increase of concentration of the salt water proves, as mentioned 

 already above, apparently the dependence of Artemia in this relation 

 principally on the reduction of air-capacity of such a water, even if the 

 giU-sacs, according to their location and formation, as it were, in these 

 animals represent modified organs of locomotion. It remains for the 

 physicists to determine how considerable is the solubility (the coeificient 

 of assumption or of capacity) of the oxygen of the air in salt water- when 

 the variation of its concentration varies. In relation to this I can find no 

 accurate data. 



III. — The genera Artemia atmd Branchipus, and the relation 



OF SOME OF THEIR SPECIES TO THE SURROUNDING ELEMENTS. 



In the whole order of Piiyllopoda the species of the genera Artemia 

 and Branchipus are apparently those which are most sensitive to the 

 intiuence of the surrounding element, in such a sense that a modifica- 

 tion of the surrounding element is capable of producing in their genera- 

 tions in a pretty short time visible mutations in their forms. A change 

 of the surrounding element can even in one and the same generation 

 produce such a variation of some parts of the body that it is difficult, 

 in a state of nature, to immediately distinguish those forms which are 

 most closely allied to each other. The species of these genera have 

 been found by me mostly in salt lakes and salt ditches (Artemia exclu- 

 sively), whereby they distribute themselves in such a manner that each 

 species is peculiar to a certain concentration, and the change of this con- 

 centration in artificially domesticating their generations produces a 

 change of form in the direction towards the next species or race which 

 lives in another concentration of salt water, toward which side the 



