Note C to Page 394. 449 
facts. When applied to the animal kingdom as a whole, the 
theory is worthless; and even within the limits of mammals, 
birds, and insects—which are the classes to which Mr. Tylor 
mainly applies it—there are vastly more facts to negative than 
to support it. This may be at once made apparent by the 
following brief quotation from Prof. Lloyd Morgan :— 
It can hardly be maintained that the theory affords us any adequate 
explanation of the specific colour-tints of the humming-birds, or the 
pheasants, or the Papilionidae among butterflies. If, as Mr. Wallace 
argues, the immense tufts of golden plumage in the bird of paradise 
owe their origin to the fact that they are attached just above the 
point where the arteries and nerves for the supply of the pectoral 
muscles leave the interior of the body—and the physiological rationale 
is not altogether obvious,—are there no other birds in which similar 
arteries and nerves are found in a similar position?. Why have 
these no similar tufts? And why, in the birds of paradise themselves, 
does it require four years ere these nervous and arterial influences 
take effect upon the plumage? Finally, one would inquire how the 
colour is determined and held constant in each species. The difficulty 
of the Tylo1-Wallace view, even as a matter of origin, is especially 
great in those numerous cases in which the colour is determined by 
delicate lines, thin plates, or thin films of air or fluid. Mr. Poulton, 
who takes a similar line of argument in his Colours of Aitmals 
(p. 326), lays special stress on the production of white (pp. 201-202). 
As regards the latter point, it may be noticed that not in any 
part of his writings, so far as I can find, does Mr. Wallace allude 
to the highly important fact of colours in animals being so 
largely due to these purely physical causes. Everywhere he 
argues as if colours were universally due to pigments; and in 
my opinion this unaccountable oversight is the gravest defect 
in Mr. Wallace’s treatment both of the facts and the philosophy 
of colouration in the animal kingdom. For instance, as regards 
the particular case of sexual colouration, the oversight has pre- 
vented him from perceiving that his theory of “ bril.iancy” as 
due to “asurplus of vital energy,” is not so much as logically 
possible in what must constitute at least one good half of the 
facts to which he applies it—unless he shows that there is some 
connection between vital energy and the development of stria- 
tions, imprisonment of air-bubbles, &c. Lut any such connection 
* Gg 
