230 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



by M. Vladimir Schmankewitsch, who conducted the 

 experiments, and though continued for only a few 

 weeks, a change in the direction of A. salina was very 

 apparent. Led by these experiments, he tried still 

 others. Taking Artemia salina, which lives in brine of 

 moderate strength, he gradually diluted the water, and 

 obtained as a result a form which is known as Branchi- 

 necta schcefferii, the last segment of the abdomen hav- 

 ing become divided into two. Nor is this change pro- 

 duced by artificial means alone. The salt pools near 



f 



Odessa, after a number of years of continued washing, 

 became converted into fresh-water pools, and with the 

 gradual change in character, Artemia salina produced 

 first a species known as Branchinecta spinosa, and at a 

 still lower density Branchinecta fer ox, and another spe- 

 cies described as B. media. Here not only new species 

 were produced, but a new genus. 



c. The Production of Colors in Lepidopterous Pupa. 



The following important contribution to this sub- 

 ject has been made by Poulton. 1 As an illustration of 

 the direct effect of the environment in the production 

 of color-changes, it is of the greatest value. Several 

 lepidopterists, among others Weismann and Merrifield, 

 had shown that by exposing the pupae of butterflies to 

 low temperatures material changes in the coloration 

 of the mature insects can be produced. Says Poulton: 

 "In 1867 Mr. T. W. Wood exhibited to the Entomo- 

 logical Society of London a number of chrysalides of 

 the large and small garden white butterflies (Pieris 

 brassicce and P. rapes], which corresponded in color to 

 the surfaces to which they were attached. Dark pupas 



1 The Colors of Animals, International Scientific Series, Vol. LXVIII, by 

 E. B. Poulton, London, 1890. 



