314 The American Naturaust. [April 
others come in their place, but these will not develop so highly, 
because the necessary food is not given. The younger forms 
have to depend from the beginning on less food, and cannot grow 
to such extent as their ancestors ; the result probably would be the 
evolution of a smaller race. This will become constant as soon as 
it is in harmony with the surroundings. We can easily imagine 
a differentiation on the same spot, through the change of condi- 
tions ; but great effects are produced by isolation. Ifa part of 
the individuals of a certain form become separated, the slightest 
difference in the conditions of the new locality must work on the 
individuals, until harmony is produced. The absence of inter- 
crossing of the separated forms will preserve the characters of 
each. I shall give an example for both cases, taken from the well- 
known communications of Vladimir Schmankewitsch. 
_ Let us imagine that the brine shrimp (Artemia salina) is liv- 
ing in a salt-water lake which is supplied with fresh water by a 
river. Through some cause this river may be prevented from — 
emptying its waters in the lake, being forced to take another course. — 
The result will be that the water will increase gradually in density. 
By this gradual change Artemia salina will be transformed into 
‘A. muhlhausenti. Of course it is impossible that any adult 
Artemia is changeable ; but the changed conditions will have an 
effect on the egg and the younger plastic stages; the old forms 
will disappear. The young ones will change until harmony with the 
surroundings is restored. Exactly the same will take place if 4 a 
salina is brought from its original locality to another place, t 
which the density of the water is greater than on the original local- De 
ity. In the first instance a new species originates on the same 
spot, through the change of conditions ; in the second a portion of Ry 
the individuals becoming isolated from the original stock devel- 
op into a new form, 
This whole consideration is based on continuous growth, and 
on the fact that members of the same form are in a differel 
stage of plasticity at a different age. If the harmony of a certain 
group is affected by the intercourse of any disturbing factor," 
other words, if the conditions are changed,—a general alarm 
raised in the group until harmony is reéstablished. Imay © 
