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504 GEOLOGICAL SURVEY OF THE TERRITORIES. 
- men would have remained comparatively short and stout in the conduct 
of these parts in the young A. salina, in which the furca is not yet de- 
veloped, or it would be in any case shorter and stouter than in the 
mature A.salina. J admitthatin further degradation of the generations 
with the characteristics of A. milhausenit the postabdomen could have 
become even, if not shorter, yet less shorter, than in the mature A. salina, 
but I only speak of what has really been the case in these specimens. The 
circumstance that at a higher salt capacity of the water, the growth of the 
degraded specimens of A. salinais going on siow, and the sexual matu- 
rity appears in time late, gives its postabdomen the chance, as if in 
contrast with the degrading influence of the element to prolcng, and 
the latter perhaps also retains the prolongation of the abdomen, espe- 
cially in combination with the heightened temperature, which also, 
according to the time, awakens the sexual maturity earlier. In A. 
milhausenti, described by Rathke! under the name of A. salina, is the 
posterior part of the body, consisting of apodous segments, also shorter 
than the anterior part, although the description, illustration, and figures 
of this author stand in great contradiction to each other. From the de- 
scription of this author it follows that this Artemia in summer lives in 
a concentration of the salt lake reaching self-deposition. Even if the 
postabdomen in our specimens with the characters of A. milhausenii is 
larger than in A. salina, there is nevertheless in transitory forms, 1n 
which the degradation did not yet reach the extreme limits, a post- 
abdomen somewhat longer than in the specimens which in the further 
generations live at a higher concentration, lacking the furca already, as 
is especially noticed in the summer generations. The length and slender- 
ness of the postabdomen prove in any case, especially in our specimens 
with the characters of A. milh., the dependence of the organization of 
these specimens upon the immediate influence of the surrounding, de- 
pendent upon the retarded development and sexual maturity appears 
earlier than the full development of body-parts, since on the whole the 
postabdomen of these forms is longer and slenderer than in the young, 
and also even in the mature forms of Art. salina. 
Contrarily the gill-sacs also prove the retarded developmeni of A. 
milhausenvi if they are also in their development simultaneously adapted 
to the demands of the surroundings. That is, in young specimens of 
A. salina exists a period in which their gill-sacs have nearly the same 
form as in the mature individuals with the characters of A. milhausenit. 
Likewise the gill-sacs are in the mature individuals with the characters 
of Art. milk. larger than in mature individuals of A. salina, especially 
in relation to width and in the comparison with the length of the body 
in these or those individuals. 
But the young individuals of A. salina now have larger gill-saes than 
the full-grown ones, there being a period in their development in which 
the gill-sacs are in length and width soin proportion, as is the case in ma- 
ture specimens with the characters of A. milhausenit. This apparently 
points to the exclusive dependence of the gill-sacs upon retarded devel- 
opment of the form in the latter specimens, but this only seems to be 
so. If we domesticate generations of A. salina in gradually diluted 
salt water this period appears, during which the gill-saes of the young 
Artemia have the measure of the gill-saes of the mature specimens with 
the characters of A. milhausenti, always earlier, 2. €., it approaches the 
beginning of development; in the domestication of these generations 
_inan opposite direction, this period always appears later; 7. e., it ap- 
11, Rathke, Beitrig. zur Fauna der Kvim. pp. 395 to 401. 
