PLATEAU'S EXPERIMENTS. 155 



ing. By accustoming fully grown specimens of this species to 

 water to which he constantly added salt, he brought them to 

 live and lay eggs in pure sea-water. The young sea-lice born 

 in fresh water died much sooner, according to him, than the old 

 ones, when both together were suddenly transferred to sea- water. 

 "While the young fresh-water lice lived only five hours when 

 put into sea-water, the young ones which had been born in water 

 already salt lived about 108 hours. Whether they died for 

 lack of food or from the effects of the salt is not determined. 

 But even if we arbitrarily assume that tlie salt was in this case 

 really the cause of death, it nevertheless results from the data 

 above given that at any rate the injurious effects of the salt arc 

 different at the two different ages of the same animal ; and, 

 secondly, that the injurious effect on young individuals can 

 be materially diminished when the older and sexually mature 

 individuals are accustomed to the strange element and breed 

 in it. These experiments, as well as those of Beudant, ought to 

 be repeated in a methodical manner ; but, imperfect as they 

 are, they teach us that many aquatic animals can be accustomed 

 to a foreign medium, and can even propagate in it. Now, 

 although, in consequence of the imperfection of these experi- 

 ments, no extensive application of this conclusion is possible, 

 they still allow of our propounding the view that it can no 

 longer be said to be impossible to accustom certain fresh-water 

 species perfectly to live in the sea, or, on the other hand, 

 marine species to live in rivers or lakes. 



A. still higher interest attaches to the recent experiments of 

 Sclimankewitsch. The fresh-water Crustacean, Branchipus stag- 

 nalis (fig. 41, a) is remarkably like the Artemia salina (fig. 41, 

 b), one of a genus otherwise found exclusively in the salt lakes 

 of America, Europe, and Africa. Nevertheless the differences 

 between them have always seemed sufficiently conspicuous to 

 justify their separation into two different genera; these are cer- 

 tain dissimilarities in the shape of the antenna? of the male, and 

 the number and form of the posterior segments of the body, of 

 which A rtem ia has but eight while Branchipus has nine. 62 There 

 are numerous species of Artemia in Europe. The most unlike are 

 Artemia salina and A. Milhausenii : the latter is distinguished 



