504 GEOLOGICAL SURVEY OF THE TEERITOEIES. 



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. 1 admit that in further degradation of the generations 

 with the characteristics of ^. wii/iawse^jn 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. salina is going on slow, and the sexual rjatu- 

 rity appears in time late, gives its postabdomen the chance, as if in 

 contrast with the degrading influence of the element to prolong, 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, aw^akens the sexual maturity earlier. In A. 

 milhaiisenii, described by Rathke^ under the name of A. salina, is the 

 posterior part of th-e 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 si)ecimens with the characters of A. milliausenii is 

 larger than in A. salina, there is nevertheless in transitory forms, in 

 Avhich the degradation did not yet reach the extreme limits, a ])ost- 

 abdomen somewhat longer than m the specimens which in the further 

 generations live at a higher concentration, lacking the furca already, as 

 is especially noticed in the summer (■enerations. The length and slender- 

 ness of the posrabdomen prove in any case, esi)ecialiy in our specimens 

 with the characters of A. rnilh., the dependence of the organization of 

 these specimens upon the immediate influence of the surrounding, de- 

 pendent upon the retarded development aud sexual maturity appears 

 earlier than the full development of body-i^arts, since on the whole the 

 postabdomen of these forms is longer aud sleuclerer than in the young, 

 and also even in the mature forms of Art. salina. 



Contrarily the gill-sacs aleo ])rove the retarded developmen:: of A. 

 milliausenii 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 i)eriod in vrhich tiieir gill-sacs have nearly the same 

 form as in the mature individuals with the characters of A. milhausenii. 

 Likewise ihe gill-sacs are in the nmture 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-sacs than 

 the full-grown ones, there being a period in their de\^elopmeut in which 

 the gill-sacs are in length and width so in proportion, as is the case in lua- 

 tnre specimens with the characters of A. milhausenii. 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-sacs of the young 

 Artemia have the measure of the gill-sacs of the mature specimens with 

 the characters of ^4.. milhausenii, always earlier, i. e., it approaches the 

 beginning of development -, in the domestication of these generations 

 in an opposite direction, this period alwaj'^s appears later; i. e., it ai3- 



' H. Ratlike, BeitrJig. zur Fauua tier Krim. pp. 395 to 401. 



