45 
was found in the scales of the white and coloured Pierids. The 
production of the yellow Pierid pigment by heating uric acid with 
water in sealed tubes at high temperatures, suggests two important 
ideas:—(1) That we have here the reason of the frequent yellow 
aberrations of white species of Pieridae, and the general tendency for 
tropical Pierids to be more richly coloured. (2) That temperature, 
acting directly on the pigment-factor of the scale at the time of its 
formation in the pupa, may exert a direct influence on the coloration 
of the scale, however normal the life of the insect may have been up 
to the point of scale-formation, that is, throughout the egg, larval, 
and early pupal stages. We learn, too, that this Lepidotic acid, 
as the yellow Pierid pigmentary matter is termed, is closely related to 
a red product, easily obtainable, and, since these three tints are the 
chief colours that function in the ornament of the Pieridae, it is 
evident that the matter is of considerable importance. 
The various work that has been done recently in the directions 
here indicated, is of the greatest value in explaining the development 
of insect colours. As I have before pointed 0 ut, any abnormal 
external force or condition, which acts upon an insect in any stage, 
and reduces its normal conditions of health, or, in fact, alters the 
normal conditions of existence at all—whether that force be heat, cold, 
or any other factor—will result in the production of an abnormity in 
some form or other Avhen it reaches the imago state. It is well-known 
that larvae, kept under unhealthy conditions, frequently produce 
crippled, ill-shapen, poorly scaled, and ill-pigmented imagines. We 
have now, as I have just indicated, a reasonable explanation of the 
transparent and pale patches sometimes found on insects’ wings, for 
we see that if the development of the scales be retarded when in the 
(1) transparent, (2) white, (3) or yellow stage of development, the 
imagines will present aberrational characters in these various 
directions. We have now simple explanations of phenomena, for 
which no satisfactory explanation was offered until recently. 
Another point worth referring to in connection with this subject 
is the recent evolution of our knowledge concerning the processes of 
histolysis and histogenesis. That histogenesis took place within the 
pupa was well known, for it was evident to everyone who studied 
insects at all, that the perfection of the imaginal tissues took place 
within the pupa ; but of the process of histolysis, by which the pupal 
tissues were first broken down before being rebuilt into the imaginal 
tissues, very little was known, and, even now, some points in the 
process are somewhat obscure. Had I been fully aware of the value 
of these processes when I wrote my Melanism and Melanochroism in 
British Lepidoptera, many references to Mr. Merrifield’s temperature 
experiments which occur would probably have been much modified. 
The fact that, during the actual process of scale-formation, you can 
retard or hurry, not only the formation of the scale, but also influence 
the nature of its contents, is evident, and, allowing the larva to have 
been brought up under the most normal conditions, the fact that you 
can bring direct external influences to bear on the developing imago, 
and mark the result on the emergence of the imago, must give 
us evidence of the most powerful kind, especially in the case of sea¬ 
sonally dimorphic insects (affected by heat and cold), as to the part 
