148 BIOLOGICAL LECTURES. 



order of causation in their conclusions, or give only more or 

 less partial statements of their results. 



The most famous case is that of Schmankewitsch's experi- 

 ments on Artemia and Branchipus, which you will, I know, 

 pardon me for sketching over hastily in order to give weight 

 to this criticism. This Russian worker on one occasion, after 

 the accidental breaking down of the dams that defended the 

 salt pans near Odessa from the uncontrolled influx of the adjoin- 

 ing brackish waters, observed that the flood brought with it Arte- 

 mia mulhauseni in great numbers, and also destroyed A. salina 

 of the dense salt water previously occupying the pans. It 

 struck this keen observer that the conversion of A. mulhauseni 

 into A. salina might be determined by following closely the 

 changes that would take place after the dam was repaired, and 

 the conversion of the outside brackish water into dense salt 

 water was begun by evaporation. He not only followed these 

 changes successfully, but he also carried on a parallel series of 

 experiments in aquaria. 



In both the natural and artificial experiments A. mulhau- 

 seni of the natural brackish waters changed into A. salina of 

 the denser salt waters of the pans after evaporation. Then 

 Schmankewitsch, by inverting the process and diluting the salt 

 water in his aquaria, succeeded in not only producing A. mul- 

 hauseni again, but proceeded farther, and by decreasing steadily 

 the amount of salt in the solution, evolved artificially Branchipus 

 of the fresh waters. The modifications of these crustaceans were 

 mainly produced in the swimming organs, especially the form 

 and hairiness of the end of the abdomen, and also the final 

 appearance of an additional segment in the abdomen of Bran- 

 chipus. Schmankewitsch at first attributed these modifications 

 wholly to the effects of the proportionate amount of salt in the 

 water as determined by its density, and subsequently appears 

 to have modified this opinion, allowing that temperature and 

 proportionate amount of oxygen contained in water of different 

 densities might have also been factors in producing the varia- 

 tions observed. 1 



1 Zeitschr.f. iviss. Zool., vol. xxv, Supplement, 1875, P- IO ^5 an< ^ Ibid., vol. xxix, 

 1877, p. 429. 



