THE INTERNAL STRUCTURE OF THE LEPIDOPTEROUS PUPA. 79 



Biding) which fills the scales destined to become pigmented, now 

 enters them. It does not enter scales which will finally be white (due 

 to air contents), but does, in many insects, enter other scales, which 

 are ultimately white. Mayer says the haemolymph of the chrysalis, 

 which is a clear amber yellow fluid, now enters them, but Chapman 

 has already adversely (Ent. Bee, ix., pp. 78-79) criticised this view, 

 and has suggested that only a secretion of the haemolymph does so. 

 The material in the scales now becomes " ochre-yellow " in tint, what- 

 ever their ultimate colour is destined to be, and, having remained in 

 this stage for about 24 hours (in the case of A. archippus), the mature 

 colours begin to show themselves. These mature colours always 

 appear first within scales which are situated between the nervures. 

 They are faint at the beginning, but gradually increase in intensity. 

 For example, if a scale be destined to become black, it first becomes 

 pale greyish-brown, and this colour gradually deepens into black i . 

 This pigment is no doubt derived from the haemolymph within the 

 scale at the time it first appears. It is probably produced by chemical 

 processes that are somewhat analogous to the clotting of the blood, for 

 the pigment is found to be sublimed over all the surfaces of the cavity 

 of the scale, the layer of pigment being especially thick upon the upper 

 surface of the scale. 



Landois, in 1864, found that when the blood of beetles and butter- 

 flies was allowed to evaporate in the air, crystals separated out. He 

 also found that the blood consisted chiefly of egg-albumen, but that 

 globulin, fibrin and iron were present. He further observed, that when 

 the blood was allowed to dry in the air, it generally became brownish 

 or yellowish, and that, while the colours of the blood were different for 

 different species, the colour assumed by the dried blood was apt to be 

 similar to the ground-colour of the wings of the mature insect from 

 which the blood was drawn. 



Mayer states that he believes the pigments of the scales are derived 

 from the haemolymph, or blood of the chrysalis ; and his chief reason 

 for believing this is, that he can find no evidence that there is anything 

 but haemolymph within the scales during the time that the pigment is 

 formed. Chapman doubts whether the crude haemolymph ever enters 

 them, but thinks that a secretion from it does so, and that the latter 

 contains the materials necessary for going through the chemical 

 change resulting in pigmentation. 



Mayer has made a chemical analysis of the pupal blood, which agrees 

 with that made by Landois. When the haemolymph is agitated with 

 ether, the proteid substances are coagulated, and a clear amber-yellow 

 solution is left. When thus isolated the proteids are slightly yellowish, 

 but they soon dry into a drab-coloured mass, very much as the haemo- 

 lymph does upon exposure to the air. Spectrum analysis shows that 

 the colour of the amber-yellow solution is due to xanthophyll, and 

 Poulton found that the colours of many lepidopterous larvae and 

 pupae were due to chlorophyll and xanthophyll, derived from their 

 food. The haemolymph is acid to litmus, and contains a large 

 amount of orthopbosphoric acid. The mineral bases of the haemolymph 

 are iron, potassium and sodium — the iron in considerable quantity. 



f This fully bears out our contention as to " pigmentary blacks." — Brit. Noct., 

 ii., pp. vi — vii ; Ent. Record, vi., pp. 38-40 and pp. 107-111. 



