﻿342 THE ENTOMOLOGIST. 



but to a retrogressive modification of yellow or chestnut into 

 white pigment, — then I admit that in Melanargia galatea we have 

 a glaring difficulty. But, granting my theory, the difficulty is 

 apparent only. 



Let me explain this. It is admitted pretty generally that the 

 pigments of animals, and of flowers also,* are, physiologically 

 considered, waste products. At any rate it can hardly be doubted 

 that they are decomposition products, due to the breaking down 

 of a large and complex molecule into several less complex. In 

 vegetable physiology it seems pretty well established that the most 

 various substances — as starch, mucilage, tannin, resin, gum, oil,f 

 &c. — are all formed by a decomposition of the protoplasm that is 

 incessantly going on ; and it is only in accord with all analogy and 

 observation to expect that the chlorophyll (or rather its forerunner 

 etiolin, or perhaps a mother-substance of this) is either a direct 

 decomposition product of the protoplasmic molecule,! or a simple 

 compound of such decomposition product with another body 

 found in the cell ; and the various plant pigments — or at least 

 many of them — are closely related to chlorophyll. Similarly, in 

 animals, it is very probable that such pigments as bilirubin, 

 urobilin, lutein, &c, are derivatives of haemoglobin, which is no 

 doubt a decomposition (katabolic) product of the protoplasm.§ 

 I have quoted the above facts to show that I am only assuming 

 that there holds good for insect pigments what is an universal 

 phenomenon of plrysiology ; and now I can state very simply 

 what seems to me the explanation of the reaction with galatea. 

 I take it that in this species the metabolic processes have not yet 

 produced any pigment, but very nearly so ; that there exists in the 

 wing a very unstable mother-substance (itself a decomposition 

 product, whether produced immediately from the protoplasmic 

 molecule, or mediately from a molecule of intermediate com- 

 plexity) ; and that the action of any powerful reagent is to 

 decompose this into a yellow pigment, and something else that 

 does not concern us at present. This view, although at present 

 necessarily somewhat hypothetical, || offers a satisfactory explana- 

 tion of the apparent anomaly in galatea.% One objection may 



* " The colouring matters of plants may be regarded simply as waste 



products in so far as their direct use in constructive metabolism is concerned." — 

 (Vines' ' Physiology of Plants, p. 242.) 



t Cf., e.g., Vines' ' Physiology of Plants,' passim; &c. 



\ Vines' ' Physiology,' p. 241. Also Dr. Schunck, on the " Chemistry of 

 Chlorophyll," in ' Annals of Botany' vol. iii. ; and of an abstract in the Microscopic 

 Society's journal for this year, pp. 196, 197. 



§ Cf. Michael Foster's ' Text-Book of Physiology,' passim. 



|| I hope before long to have an opportunity of examining these various pig- 

 ments by a method sufficiently obvious, which I hope may give us a far clearer 

 insight into their constitution and affinities. 



*\ It is of course an essential corollary from this that galatea may be expected 

 one day to become yellow, — by perfecting its decomposition processes ! As a matter 

 of fact I may point out that already (in the female) the presence of the "mother- 

 substance " of the pigment has produced a slight yellowish-cream tinge. 



