BRITISH LEPIDOPTERA. 



" The freshly-obtained haemolymph is a clear opalescent amber-yellow 

 fluid ; it soon becomes turbid upon exposure to the air, and in less 

 than half-an-hour after removal from the chrysalis becomes opaque, 

 and drab or greenish-drab in colour. " Mayer further notes that the 

 drab colour, assumed by the dried haemolymph obtained from the pupa 

 of Callommia promethea, and the greenish-drab assumed by the dried 

 haemolymph of Philosamia cynthia, are very similar to the principal 

 colour of the moths' wings. The change in colour exhibited by the haemo- 

 lymph upon exposure to the air is probably not due to a simple process 

 of oxidation. It takes place slowly in an atmosphere of hydrogen ; an 

 atmosphere of CO 2 prevents it ; whilst, if the haemolymph be sealed 

 up in air-tight glass tubes, it retains its amber colour indefinitely. 

 Heated to 54°C, it begins to congeal, and above 63°C. solidifies into a 

 chrome-yellow mass, and, in this condition, it will keep indefinitely, 

 and retain its original chrome-yellow colour ; but when congelation is 

 produced in haemolymph that has become drab by exposure to air, the 

 congealed mass is also drab in colour. 



To test whether the colours of the mature wing are derived by 

 various chemical processes from the haemolymph of the pupa, Mayer 

 performed the following experiments : (1) He treated the haemolymph 

 of Samia cecropia with warm concentrated HNO g , when it congealed 

 into a deep chrome-yellow mass. Ammonia (in excess), added to this, 

 changed it to reddish-orange, very similar in colour to the reddish- 

 orange band that crosses the upper surface of the hindwings of the 

 moth. The reddish -orange band of the moth is changed to chrome- 

 yellow by HC1 or HN0 3 , and, on ammonia being added, the original 

 red colour returns. Exactly the same sequence of reactions is produced 

 with the pigment derived from the haunolymph. (2) Treating the 

 drab-coloured outer edge of the wing of S. cecropia with warm HN0 3 , 

 and evaporating the acid off at a gentle heat, the drab pigment of the 

 scales was found to be changed to a deep chrome-yellow. The addition 

 of ammonia makes it reddish. Similar reactions are obtained from 

 the haemolymph, after'it has congealed in the air into a greenish-drab 

 mass. (3) The drab haemolymph of Callosamia promethea is dissolved 

 and changed to a sepia-broAvn colour by warm HC1, to which a crystal 

 of KC10 3 is added. An exactly similar change occurs when the drab- 

 coloured edges of the moth's wings are treated in a similar manner. 



These experiments, like those of Coste (Entomologist, 1891, et seq.) 

 and Urech (Zeit.f. iciss. Zool., lvii., 1893-1894), get no further, in 

 fact, not so far, in relation to the white pigmentary scales as Coverdale 

 and ourselves got some twelve years ago (Brit. Noct., vol. ii., pp. iii — 

 xviii) . A brief statement of the general action of alkalies in changing 

 pigments, and of acids in restoring the changed pigments to their 

 original colours, was published by Coverdale (Entom.) in 1886. 



As to the chemical nature of the pigment in the scales, we know 

 but very little. Hopkins has shown that the white pigments in the 

 Pieridae are due to uric acid. Mayer quotes this, and yet seems to 

 have failed entirely to apply the self-evident deductions to his own 

 observations on the white scales. Throughout his paper we read 

 nothing of the pigments in the white scales of certain butterflies, 

 but the general assumption is more than once expressed, that the 

 colour of all white scales is due to their being devoid of pigment and 

 to the reflection of light. Hence the justice of Chapman's criticism 



