to 6, into that of A. Milhausenii; 7, post-abdomen of A.
salina; 8, post-abdomen of a form bred in brackish water; 9, gill of A.
Milhausenii; 10, gill of A. salina. (From Schmankewitsch.)]

_Semper on the Direct Influence of the Environment._

Another eminent naturalist, Professor Karl Semper of Wuerzburg, also
adopts the view of the direct transforming power of the environment, and
has brought together an immense body of interesting facts showing the
influence of food, of light, of temperature, of still water and moving
water, of the atmosphere and its currents, of gravitation, and of other
organisms, in modifying the forms and other characteristics of
animals.[207] He believes that these various influences produce a direct
and important effect, and that this effect is accumulated by
inheritance; yet he acknowledges that we have no direct evidence of
this, and there is hardly a single case adduced in the book which is not
equally well explained by adaptation, brought about by the survival of
beneficial variations. Perhaps the most remarkable case he has brought
forward is that of the transformation of species of crustaceans by a
change in the saltness of the water (see Fig. 35). Artemia salina lives
in brackish water, while A. Milhausenii inhabits water which is much
salter. They differ greatly in the form of the tail-lobes, and in the
presence or absence of spines upon the tail, and had always been
considered perfectly distinct species. Yet either was transformed into
the other in a few generations, during which the saltness of the water
was gradually altered. Yet more, A. salina was gradually accustomed to
fresher water, and in the course of a few generations, when the water
had become perfectly fresh, the species was changed into Branchipus
stagnalis, which had always been considered to belong to a different
genus on account of differences in the form of the antennae and of the
posterior segments of the body (see Fig. 36). This certainly appears to
be a proof of change of conditions producing a change of form
independently of selection, and of that change of form, while remaining
under the same conditions, being inherited. Yet there is this
peculiarity in the case, that there is a chemical change in the water,
and that this water permeates the whole body, and must be absorbed by
the tissues, and thus affect the ova and even the reproductive
elements, and in this way may profoundly modify the whole organisation.