iv SCHMANKKWITSCH'S EXPERIMENTS 213 



But external differences seem in some cases to have 

 much greater moment than has hitherto been re- 

 cognised, and in this respect no facts are of higher 

 interest than those which were some years ago made 

 known by the investigations of a Russian naturalist, 

 M. Schmankewitsch, 1 to whose work I must call 

 attention, although most have certainly heard more 

 or less about it. Daphnia (or Moina) rectirostris is a 

 small Crustacean which lives indifferently in fresh 

 water, in brine ditches, and in salt lakes when the con- 

 centration varies from five to eight degrees of Baume's 

 areometer. But this difference in life-conditions is 

 .accompanied by noticeable variations in the physiology 

 and structure of the animal. The mean temperature of 

 the salt lake being lower than that of the fresh waters, 

 Daphnia while being a summer form in the latter 

 becomes an autumn form in the former, and thus 

 has acquired the custom of living and even multiply- 

 ing in salt water at temperatures at which the fresh- 

 water form cannot live. So much for the physiological 

 variation. M. Schmankewitsch goes on to say, as 



(Schriften der Naturforschenden Gesellschaft zu Dantzig, 1888). Both 

 authors obtain results which are entirely confirmed by M. Lesage's 

 investigations. 



1 Cf. Zeitschrijt f. Wiss. Zoologie, 1877, vol. xxix., p. 429, and also 

 the Transactions of the Neo- Russian Society of Naturalists for 1875. 

 The original papers have been abstracted in Packard's Monograph of 

 North American Phyllopod Crustacea, 1883, Washington (Geological 

 Survey). 



