v INTRODUCTION. 



white, and their pigments readily bleach, although the brighter red 

 of urticce is perhaps more rapidly soluble, showing that the greater 

 elaboration tends to greater solubility. Strong ammonia dissolves 

 the red of urticce very speedily. It results, therefore, that the 

 brighter colour of urticce is due to a fuller, and probably more 

 rapid, development of the pigment in the pupal stage, and that, if the 

 formation in the pigment in urticce be stopped in the process of its de- 

 velopment from the pigment-producing material, that the less perfectly 

 developed colour would result. Further than this, since we must 

 assume that the waste product which is to form the pigment has been 

 stored up in the larval stage, and simply undergoes elaboration in the 

 pupal stage, it follows, that the less highly developed colour, i.e. the one 

 which is produced by the least elaboration, must be the result in those 

 instances where the vital processes are for the time being, stopped, as is 

 undoubtedly the case when the pupas are subjected artificially, or other- 

 wise, to a very abnormally low temperature. This would readily account 

 for the production of the dull coloration in the ill-developed urticce 

 before mentioned, and the tendency of the dark ground colour to 

 occupy the space usually filled up by the pigmentary structures. 



That the apparent result will not always be the same in different 

 species, and that sometimes this incomplete development of pigment may 

 tend to produce a duller (darker?) and sometimes a paler imago, is readily 

 seen ; but, it is clear, that in all cases, an obsolescence or tendency to 

 obsolescence of positive markings must ensue. For example, the pig- 

 ment may be produced in scales having a base or framework of white 

 or black (or, in fact, any other colour). In other words, the colour of 

 the scale is independent of the colour of the base. Now, if we dissolve 

 all the pigment from the yellow portion of the wing of Colias edusa, 

 the resultant wing is white, whereas, if we dissolve the pigment of 

 Vanessa io, the resultant colour is black. Hence, a retrogression of, 

 or failure to develop pigment in the former, must, I think, tend to 

 produce dull, whitish specimens ; the retrogression in the latter to 

 produce black specimens with a more or less diaphanous tendency. 

 The normal colour of the basement structure of the wing must, there- 

 fore, have a considerable influence on the net result. 



In the same way, it results that retrogression in the case of Vanessa 

 urticce ends in darkening the ground colour, in other words, of increasing 

 the dark at the expense of the bright colours of the wing, and also 

 frequently in the simultaneous change of the bright meteor-red into an 

 approach to the duller polychloros-red. On the other hand, I consider 

 the black form the most highly developed pigment coloration, in a 

 species like Tceniocampa instabilis. It has reached this form through 

 brown, red and ochreous from white. Here, then, retrogression would 

 tend to produce a pallid coloration, thereby having a diametrically 

 opposite tendency, in a gradual change, from what results in Vanessa 

 urticce. 



To refer to another point. In the Introduction to Vol. i., p. 

 xiv. I just mentioned that Lord Walsingham had suggested that any 

 cause tending to lessen the proportion of chemical rays of the sun 

 reaching the earth in any particular locality, might influence the colour 

 of lepidoptera. Mr. Merrifield, by feeding larvae under differently 

 coloured glasses, and by filtering light through bisulphide of carbon 

 &c., attempted to get some results in this direction. When giving an 



