A8() GEOLOGICAL SURVEY OF THE TERRITORIES. 
of the salt water, only inhabitable by Artemia, and especially at suffi 
cient warmth, the mature sexual products show themselves already at a 
time when the provisional parts of the second, lower antennz were 
scarcely dropped, @. 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 for Branchipus. Between the fresh-water Branchipide and 
those Artemie 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- 
mice, already in their larval stage, but in any case in the last period of 
the latter, before the sécond antenne 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 
that this is applicable to those Artemiz 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 progressive 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 propagation 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 129° 
Beaumé’s areometer and with summer temperature; the highest devel- 
opments of bedy-parts I noted at 5° to 7° Beaumé, and at the same tem- 
perature. 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 propagation 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 viviparous reproduction in Ar- 
temia salina in stronger saline water at such a low temperature at which 
viviparturition in the same species 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 Branchipodide, 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 
1**Revue scientifique de la France et de l’étrang.,” 2. series, 1873, No. 27, pp. 632 to 
633. Also in ‘‘Meeting of Swiss Naturalists” in Freiburg i 1. 8., 1872. 
