1395.] Fluorine as a Test for the Fossilization of Animal Bones. 439 
changes in the individual, in other words, that the definite 
current of variation is guided by the inheritance of individual 
reactions and not by some other principle. 
Another consideration is, that individual Variation may play 
a far less conspicuous rôle than we have assigned to it; in 
other words, that many of the most important changes in suc- 
cessive generations are so gradual as to be entirely inconspicu- 
ous in a single generation. 
Our conception of the mechanism or physical basis of Hered- 
ity is also to be made much clearer by a series of experiments 
directed to palingenic variation, in order to ascertain how far 
the revival of an ancient environment arouses latent hereditary 
forces. The experiments already well advanced by Cunning- 
ham, Agassiz, and Poulton indicate that progressive inheritance 
is rather a process of substitution of certain characters and potential- 
ities than the actual elimination implied by Weismann. 
My last word is, that we are entering the threshold of the 
Evolution problem, instead of standing within the portals. 
The hardest tasks lie before us, not behind us, and their solu- 
tion will carry us well into the twentieth century. 
Columbia College, New York. 
ON THE PRESENCE OF FLUORINE AS A TEST FOR 
THE FOSSILIZATION OF ANIMAL BONES. 
By Dr. THomas WILSON. 
(Continued from page 317, Vol. XX IX.) 
It is interesting to examine closely this question, and, for 
that purpose, critical analyses have been made of a large 
number of bones of different geological ages. The fluorine 
and phosphoric acid have been determined with exactitude 
and the proportion of the quantity of fluorine found in the 
bones to that which apatite, having an equal quantity of 
phosphorus would contain, has been calculated. The calcula- 
tion of the fluorine of apatite is easily made by multiplying 
the weight of the phosphoric acid by the co-efficient 0.0892 
which expresses the normal proportion oF 
3P,0, 
