10 BK1TISH LEPIDOPTEKA. 



the larger eggs produce females, the smaller, males. Hellins observes 

 that of about twenty-three eggs laid by a female Smerinthus populi, the 

 last laid eggs were only two-thirds of the size of those first laid. Chapman 

 has recorded that there is considerable variation in the size of eggs laid 

 by the various species of Acronyctid moths. In Triaena tridens there are, 

 apparently, at least two races which lay differently sized and differently 

 ribbed eggs, whilst the eggs of Pharetra euphorbiae var. myricae also 

 vary very much in size. 



The eggs of Lepidoptera do not vary much in colour when first 

 laid. They are usually whitish, pale yellow, or pale greenish in tint, 

 but, after they are laid, they change colour very quickly, and the 

 colour then probably becomes of that hue which will most exactly 

 harmonise with the surroundings among which the egg is usually laid. 

 The eggs of Thecla w-album are laid above, or directly below, 

 an aborted leaf -bud, and harmonise so exactly with the colour of the 

 bark of the elm-twig on which they are placed, that only an entomolo- 

 gist could possibly detect them. They appear to be placed always on 

 the old, and not on the growing twigs, and thus everything tends to 

 aid in their protection. 



The first colour-change of the lepidopterous egg usually takes 

 place within a few hours (12-72) of an egg being laid. After this first 

 colour-change, many eggs undergo a whole series of complicated colour- 

 changes, due to the development of the embryo within, the changes being 

 easily followed through the transparent egg-shell. Eobson says that the 

 change of colour of the newly-laid Hepialid egg, from white to black, is a 

 change in the colour of the shell only, and this is so, for the egg-shell 

 remains black after the young larva has left the egg. Many eggs, 

 however, like those of the Hepialids, change colour but once (directly 

 after being laid). The egg of Euchloe cardamines is yellow when laid, 

 becomes deep orange in about twenty-four hours, and, with the excep- 

 tion of a slight change just before hatching, remains of this tint. The 

 egg of Endromis versicolor is pale green when laid, rapidly becomes 

 yellow, then changes to orange, and finally to purple. Jordan records 

 an opaque white egg of Centra vinula, instead of the usual chocolate- 

 coloured egg. Hellins observes that eggs of the same species vary 

 in colour, and do not always go through the same changes of colour 

 when approaching maturity. He instances Oryyia antiqua, Centra 

 vinula, Hepialus sylvinus, and Cheimatobia bntmata. The changes 

 which Chapman has chronicled as taking place in the Acronyctid 

 eggs while maturing, are exceedingly interesting. These changes may 

 vary according to temperature, the colouring of Pharetra rumicis, 

 which is assumed in two days in warm weather, taking a week in cool 

 weather. The egg of Leucania Uttoralis is at first pale yellow, then it 

 becomes orange, then mottled with reddish, and at last slightly 

 purplish, at which stage the shell itself is seen to be perfectly trans- 

 parent, and the embryo may be observed within the egg-shell. The 

 egg of Acontia luctuosa is pale yellow, then whitish with a row of red- 

 brown spots just above its equator. The egg of Phytometra viridaria 

 is pearly white, then it develops two bright claret-coloured rings, one 

 of which surrounds the micropylar area and the other the shoulder of 

 the egg ; after this the red areas become enlarged, and tend to join. 

 Many eggs exhibit a similar wide series of colour-changes during 

 the development of the embryo. 



* Entom. Record, etc., v., pp. 140-146. 



