306 Evolution and Adaptation 
crustacean, Branchipus ferox, the form differs in a number 
of points, according to whether it lives in salt or in fresh 
water. Schmankewitsch says that, had he not found all 
transitional forms, and observed the transformation in 
cultures, he would have regarded the two forms as separate 
species. The oft-quoted case of Artemia furnishes a very 
striking example of the influence of the environment. 
Artemia salina lives in water whose concentration varies 
between 5 and 12 degrees of saltness. When the amount 
of salt is increased to 12 degrees, the animal shows certain 
characteristics like those of Artemia mitlhausenit, which 
may live in water having 24 to 25 degrees of saltness. The 
form A. salina may be further completely changed into that 
of A. milhausenit by increasing the amount of salt to the latter 
amount. 
Among domesticated animals and plants—a few instances 
of which have been already referred to— we find a large 
number of cases in which a change in the environment 
produces definite changes in the organism. Darwin has 
made a most valuable collection of facts of this kind in his 
“Animals and Plants under Domestication.” He believes 
that domesticated forms are much more variable than wild 
ones, and that this is due, in part, to their being protected 
from competition, and to their having been removed from 
their natural conditions and even from their native country. 
“In conformity with this, all our domesticated productions 
without exception vary far more than natural species. The 
hive-bee, which feeds itself, and follows in most respects 
its natural habits of life, is the least variable of all domesti- 
cated animals.... Hardly a single plant can be named, 
which has long been cultivated and propagated by seed, that 
is not highly variable.” ‘‘ Bud-variation . . . shows us that 
variability may be quite independent of seminal reproduc- 
tion, and likewise of reversion to long-lost ancestral charac- 
ters. No one will maintain that the sudden appearance of 
