130 Exper'mmdal and Statistical Studies upon Lejndoptera 
We approach the true solution of the problem, I believe, when we realize that 
we are justified in stating nothing more than that the surviving pupae or those 
which metamorphose perfectly are of particular forms, and are more conservative 
with reference to those particular foi'ms than are the individuals which succumb. 
In short, we may not say that tlie longer antennae serve the pupa in escaping 
elimination, but we are justified only in asserting that the surviving pupae have 
longer antennae. Wheu this statement is made for all the characters which 
exhibit selection, we see that the essence of fitness is a morphological conservatism 
with reference to certain values of the dimensions under consideration. Certain 
it is that those which depart widely from the " fit " type are numbered among 
the dead. 
According to this view, elimination is based upon the general or total efficiency 
of any individual. And this value is determined by the proper coordination of 
functional and structural elements. The actual basis for elimination is, in a word, 
correlation. If this be slight, a condition of less stable equilibrium arises which 
renders the particular individual less efficient, and which places it among the 
unfit. In the present case, however, we are dealing with an organism, the pupa, 
which does not use its structui es ; so that any lack of proper correlation is 
attributable to an absence of proper coordination among the formative factors 
which control the establishment of pupal structures, or by which the imago is 
constructed upon the pupal basis. 
I believe, then, that the test of fitness or unfitness has reference to the 
physiological and morphological coordination or correlation among the constituent 
elements of the whole organism, and that any relaxation in either series, in a 
formative sense or otherwise, results in an instability which may culminate in 
death and which expresses itself in structural deviation as well as in a higher 
degree of variability. 
Barnard College, Columbia University, 
November, 1903. 
