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 variability exists. They think that other fac- 
tors than concentration probably also 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 litter on board ship in the year 1418 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, 1861, I examined two of these rabbits recently sent to 
the Zodlogical Gardens, and their tails and ears were colored 
1 SchimkeWitsch (Biolog. Centralblatt, XXVI, 1906) states that Anikin (1889) 
and Butschinsky (1901) have obtained results contradictory to those of Schman- 
kewitsch. I have not seen their papers. 
