478 ; The American Naturalist. pee 
the determination of sex may be mentioned here, as well as 
those of Yung, Mrs. Treat, and others on the influence of foods. 
If an altered environment is capable of altering function—and 
we know this to be a fact—and if the altered function reacts 
upon structure—which is equally undoubted—then we find in 
these premises sufficient justification for searching after the 
facts concerning the nature and extent of environmental in- 
fluence. The value of such researches lies not so much in the 
isolated results themselves, as in the fact that such results, 
when sufficiently numerous, will lead us directly not only to a 
better understanding of the internal physiology of organisms, 
but, what is of more general interest, to an understanding of 
the causes of variation, and thus to a better comprehension of 
the relations of species to one another. Too much cannot be 
said upon this phase of our subject. Whether the direct action 
of the environment is to be considered as a factor in organie 
evolution or not, the causes of variation must be investigated 
experimentally, and the physiological side of the work must not 
e neglected. Semper says, “Although the morphological sec- 
tion of animal biology* teaches with much probability that this 
species or that organ has undergone this or that course of mod- 
ification in the animal series, and that in the process of modi- 
fication it has passed through a whole series of various forms, 
still it is only physiological research that can elucidate the 
necessity for their existence by revealing their causative con- 
itions.” . i 
One word regarding the relations of physiology and mor 
phology. In the broad way in which I have outlined the 
former science, it may be charged that I have trespassed upon 
the morphological preserve. I do not deny the charge. It 
seems to me altogether unnecessary, undesirable and moreover 
impossible to draw a sharp line of distinction between the two 
: * Siete . re E 
sciences. With a common origin, mutual independence was, 
in time, necessary to the growth of each, yet this is in ent = 
harmony with the fact that they have a common meeting” 
ground. In these days, as always, the morphologist must s 
something of a physiologist; the physiologist something ° E 
*He might justly have omitted the word “animal.” 
