n 
720 Growth and Development, i [July, 
abundance of Rhizopod food, and the incessant motions of Rhiz- | 
opods, are the two conditions through which the survival of these 
primitive life forms is attained. 
But every motion has some modifying effect upon the constitu- 
tion of the body. Response to any contact causes increased sen- 
sitiveness in the part affected. As the steel accepts magnetism 
most readily in the direction in which it has been formerly mag- 
netized, so does the Amceba respond to contact influence most 
readily in parts that have been most frequently touched, and it 
repeats most easily the special motions it has previously made. 
Of the many motions and changes of form which may occur, 
those best adapted to food-getting will be selected, since the ani- 
mals making them will survive while their competitors will perish. 
The various species of rhizopods indicate the various kinds of 
rhizopodal motion that have best succeeded in food capture 
Evolution in this early stage is first the preservation and then the 
inheritance of such results of chance deviation as have proved 
successful. é: 
The best adapted movements from danger are as important y 
the best adapted ones towards food. In the earliest life stages we 
might imagine that survival of ill-protected forms could resu 
only from retrograde movements, or from excessive reproduction. | 
It would seem as if protection by the formation of defensive | 
armor should be a late result of evolution. Yet, on the pu 
trary, armor is assumed by some of the lowest forms at aii | 
diatoms and various rhizopods. This result proves that nee 
ditions for the assumption of defensive armor exist = l : 
and arise from some native characteristic of protoplasm. = 
+. All active 
need we go far to discover the cause of this effect. aboot 
protoplasm absorbs and employs water. But the water B 
contains lime and silica in solution. As the water 15 eee 
employed these substances are precipitated, and are sid into place I 
the body in their insoluble form. Here chance apres They 
They may be washed away by the surrounding wan 
may continue on the surface, the minute particles ag& 
to a solid coating. Proving protective they are 
selection and inheritance act to the evolution of k 
Very early, then, in the animal series evolution ta par motion — 
tions. In one there isa naked body, trusting t° jas e 
for safety. In the other there is a coated body, trus 
