480 GEOLOGICAL SURVEY OF THE TERRITORIES. 



of the salt water, only inhabitable by Artemia, and especially at suffi 

 cient ■warmtb, the mature sexual products show themselves already at a 

 time when the provisional parts of the second, lower antennfe were 

 scarcely dropped, i. e., when they have not yet left the last larval stage. 

 Artemia lives a much longer time in the larval state than Branchipus^ indeed 

 the longer, the higher the concentration of the water for Artemia and 

 the lower lor Branchipus. Between the fresh-water Branchipidce and 

 those Artemia} which can still live in a salt-lake self-depositing salt, 

 there is a relative great difference. Accordingly we must allow that we 

 can produce, by corresponding domestication of generations of Arte- 

 mia\ already in their larval stage, but in any case in the last peiiod of 

 the latter, before the second antenna? have dropped their provisional 

 parts, sexual maturity. Carl Vogt's observations have shown that the 

 eyes appear much later in Artemia than in Branchipus,^ and I presume 

 tiiat this is applicable to those Artemiaj which are in relation to Bran- 

 chipides, degraded forms of the latter. 



I have to mention the circumstance that the concentration of the salt 

 water vigorously stimulates the multiplication of Artemia. The highest 

 increase of a given species of Artemia is brought about by a density of 

 the salt water which is a little higher than that generally assumed as 

 the mean for this species; therefore under such conditions which hin- 

 der, to a certain degree, the growth of the individuals and the develop- 

 ment of their body-parts. On the other hand the most rapid growth 

 and the i)rogre8sive development of body-parts happen to appear at 

 such a concentration of the salt water, which is a little below the mean 

 for a given species, and at which density the x>ropngatiou of the indi- 

 viduals decreases. In Artemia salina I observed the highest multipli- 

 cation in a state of nature at a density of the salt water of 10<^ to 12° 

 Beaume's areometer and with summer temperature; the highest devel- 

 opments of body-parts I noted at 5° to 7° Beaume, and at the sametem- 

 l}erature. Between these limits must be the mean density of the salt 

 water for our Artemia salina; I have also to remark, that the density of 

 the salt water, together with the temperature, and independently of the 

 same, influences the growth and the i)ropagation of these animals. It 

 appears that the parthenogenetic reproduction in Artemia does not only 

 depend upon the temperature, as in Daphnia, but also upon the density 

 of the salt water. I observed at least vi^dparous reproduction in Ar- 

 temia salina in stronger saline water at such a low temperature at which 

 viviparturition in the same siDCcies does not occur in less saline water, 

 although it does not hinder viviparturition at a comparatively higher 

 temperature. In all such cases the quantity of air contained in the 

 water and dependent upon temperature, as well as upon concentration 

 of the salt water, plays an important role, regulating many of the func- 

 tions of life. Perhaps the variability of the concentration of the salt 

 water yields, in Artemia, one of the main causes of parthenogenesis, 

 the latter not being yet known to occur in Branchipodidce, inhabiting prin- 

 cipally fresh water. Density and temperature of the salt water in their 

 influence upon Artemia are combined in such a manner that, when the 

 existence of an Artemia-like form in fresh water is possible, the same 

 can only exist at a nearly summer and possibly high temperature. The 

 lower the density of the salt water the higher a temperature is re- 

 quired, if Artemia shall preserve its form at least in its principal char- 

 acters. In this sense, Branchipus stagnalis, which, according to the 



' "Revue scientifiqne de la France et de I'^trang.," 2. series, 1873, No. 27, pp. 632 to 

 633. Also in "Meeting of Swiss Naturalists" in Freiburg i. s., 1872. 



