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series of this species in the British Museum, supposed to 

 represent that variety, are every one of them bleached white, 

 having been originally yellow ! 



Various chemicals, too, alkalis especially, will bleach or 

 change the colour of animal pigments ; ammonia, for instance, 

 will change the white of some Lepidoptera to yellow ; and in 

 many ways it appears that the constitution of these pig- 

 ments is very unstable, and that they are easily changed 

 from one form into another. 



A scarlet-red or pink pigment is very general through 

 many classes of animals — I mean, for instance, the red of 

 Arctia caia and the Zyg(zncB ; of some birds of the genus 

 Fringilla, as the chaffinch ; of the toad Bombinator; and of 

 the bivalve shell Tellina balthica, and the gasteropod Helix 

 n em or alls. 



Now, in nearly every, if not every case, in which this 

 peculiar red pigment occurs, there is an occasional variety 

 in which the red is replaced by yellow; and further, there 

 are very frequently normally yellow species in the same 

 genus. 



Arctia, for instance, has the species caia, which is normally 

 red, but has a yellow aberration (such as those lime-fed 

 ones we saw exhibited here at a former meeting), and villica, 

 which is normally yellow, tinged on the abdomen and under 

 side with red, except in the variety fidminans from Syria, 

 which has the yellow of the underwings wholly replaced by 

 red. 



A variety of Zyga^na filipendnla;, in which the red is re- 

 placed by yellow, is not very uncommon, and has been taken 

 at Box Hill in our district, as well as at Cambridge and 

 elsewhere. ZygcEiia trifolii lias also presented a similar 

 aberration ; and a variety of Choerocampa porcellus, which 

 might be called lulescens, having the pink replaced by yellow, 

 was obtained in Perthshire. Similarly, in the genus Sesia, 

 there are red-belted species and yellow-belted species, and 

 a variety of 5. culicifonjiis, in which the abdominal band is 

 normally red, was found with a yellow band instead, thus 

 resembling the normal colour of others of the genus. 



