PACKAKD] TRANSFORMATION OF ARTEMIA. 467 



brought along witli the flood from the upper portion as well as from the 

 surrounding brine ditches near the same. 



After restoration of the embankment the density of the. water of the 

 lower part rapidly increased, showing already in the summer of 1872 

 14°, in 1873 18°, at the beginning of August 1874, 23.5°, and after a 

 continued drought in September of the same year 2o° of Beaume's 

 areometer, at the latter time the lower part of the lake beginning to 

 deposit salt. 



[Simultaneously Artemia salina gradually degraded fi^om generation 

 to generation, so that toward the end of the summer of 1874 the majority 

 of individuals were without furcal lobes, showing then all the specific 

 characters of Artemia muehlhausenii (Fig. 6). In 1871 Artemia salina, 

 or better, one of its varieties, had moderately large furcal lobes, and on 

 each of them eight to ten, seldom 15, setse, distributed over both sides 

 and the tips (Fig. 1). 



In the successive generations in the beginning of the summer of 1872, 

 these furcal lobes were already smaller, with but 3 to 5 or 3 to 4 setee, 

 the salt water then showing 14° Beaume (Plate XXXIX, Figs. 2 and 3). 



In the same season of 1873 and at 18^^ B. the furcal lobes were still 

 smaller, representing short conical knobs with but one, two, seldom 

 three, sette (Fig. 4). Toward the end of the summer of 1874, many 

 individuals still possessed conical knobs or protuberances instead of 

 furcal lobes, without or with but one seta on tip, but the majority of 

 them were entirely destitute of furcal lobes and setss, as is the case in 

 Artemia. muelilhausenii with which these degraded examj>les were 

 identical in their smaller size as well as in other characters (Figs. 5 

 and G). 



I also obtained the same results by domesticating Artemia salina in 

 salt water of gradually increased density or concentration, the examples 

 obtained being identical with those from the Kujalinker Lake at the 

 end of the summer of 1874 (Artemia muehlhausenii), yielding also the 

 same transitory forms. 



By a reverse treatment, i. e., by gradually diluting the salt water, I 

 succeeded w^th Artemia muehlhausenii in i3roducing already, after sev- 

 eral weeks, a fnrca in the form of couic^al knobs, with one terminal 

 bristle, by which treatment also the development of other parts of the 

 body assumed a direction toward the higber specialized varieties of 

 Artemia salina, this being at variance with the retrograde development 

 taking place in condensing the salt water. 



It is remarkable that the gills of these animals enlarge in proportion 

 or in ratio with the density of the water, so that in the form without 

 furcal knobs {Artemia muehlhausenii) the surface of the gills is much 

 larger in proportion to the size of the body than in Artemia salina. The 

 gills of the former especially enlarge in width. I draw the inference 

 that as the water of higher density contains less oxygen these Crusta- 

 ceans adapt themselves by gradually enlarging the surface of the 

 breathing apparatus. 



Concerning the gills, I have to state that they are elongate in Artemia 

 salina and oval in A. muehlhausenii (Figs. 7 and 8). The width of the 

 gills in A. salina average scarcely half of their length, in A. muehl- 

 hausenii two- thirds of their length. 



As regards the length of the body, I may mention the following- 

 measurements, showing the proportionate sizes of the gills; In Artemia 

 salina the average length of the gills at a density of 10° B. is the one- 

 twenty-lirst part of the b.ody length, the width being the one-thirty-ninth 

 I)art of the same. In Artemia muehlhausenii the average length of the 



