156 



THE INFLUENCE OF INANIMATE SURROUNDINGS. 



by the absence of spines on the lobes of the tail, the small size 

 of these lobes, and the relatively large size of the branchial 

 ajspendages of the legs. Schmankewitseh showed that it was 

 possible to raise a brood of Artemia Milhausenii from Artemia 

 salina, which lived in salt water of 4° Beaume, by gradually 

 raising the percentage of salt to 25° B. This transformation 

 occurs very gradually, and only in the course of several gene- 

 rations. He observed the same process al.so in a free state of 

 nature. A dam which divided a lake containing salt water of 

 4° B. from another where the water marked 25° B. gave way 

 in the year 1871, so that the density of the water in the lower 

 lake fell to 8° B. At the same time numberless individuals of 



Fig. 41. — a, Branchipm stagnalis j b, Ariemia salina. 



Artemia salina were carried through to the lower lake by the 

 flood, and there they soon settled and propagated. After the 

 dam was repaired the saltness of the water in the lower lake 

 naturally increased again; in 1872 it had risen to 14° B., in 

 1873 to 18° B., and by the end of September 1874 it had reached 

 its old mark of 25° B. During this period the Artemia salina 

 that had migrated had gradually .become transformed into 

 Artemia Milhausenii. The stages of transformation, as they were 

 actually successively observed one after another by Schmanke- 

 witsch, are here given in a woodcut (fig. 42) copied from 

 Schmankewitsch's drawing. 



He also conducted the converse experiment with perfect 



