The Influence of External Conditions 41 



former was contained became more concentrated by evapo- 

 ration. Experimentally he procured the same result by con- 

 centration. Furthermore Schmankewitsch claimed that by 

 gradually diluting the brackish water in which Artemia salina 

 lives he obtained a form having the characters of the genus 

 Branchippus. 



These conclusions have been seriously questioned by Bateson 

 and by Samter and Heymons/ who have shown that Artemia 

 salina is subject to great individual variability and that there 

 is no close connection between the different variations and the 

 concentration of the water in which they occur. Especially 

 doubtful is Schmankewitsch's comparison with Branchippus, 

 whose diagnostic features he seems to have imperfectly under- 

 stood. Samter and Heymons find nevertheless that the salt 

 content of the water has some influence on the form of Artemia 

 salina, although in different pools of the same concentration 

 a large range of variabiHty exists. They think that other fac- 

 tors than concentration probably ako affect the result. 



Changes in Mammals and Birds 



The Porto Santo rabbits, so fully described by Darwin, fur- 

 nish another instance of influence of the environment. It is 

 said that these rabbits originated from a single pregnant female 

 that produced a fitter on board ship in the year 141 8 or 1419. 

 Set free on the island of Porto Santo, the rabbits increased 

 rapidly and soon became a pest. Darwin examined these 

 rabbits and found that, compared with domesticated rabbits 

 of average size, the Porto Santo rabbits had lost three inches 

 in length and almost half the weight of the body. In other 

 points also they differed — in the skull, and especially in 

 color. "But here we meet with a singular circumstance: In 

 June, 1 86 1, I examined two of these rabbits recently sent to 

 the Zoological Gardens, and their tails and ears were colored 



^ Schimkewitsch {Biolog. Centralhlatt, XXVI, 1906) states that Anikin (1889) 

 and Butschinsky (1901) have obtained results contradictory to those of Schman- 

 kewitsch. I have not seen their papers. 



