THE LIfE-UlSTORY OF A LEPlDOPTEROUS iNSECT. l3'J 



I believe Mr. Harwood and myself both inclined to the latter view" 

 {Ent. Mo. Mag., xix., pp. 208-209). Dr. Chapman has recorded that 

 there is considerable variation in the size of eggs laid by the various 

 species of Acronycta. Jn Cnspidia tridens, there are, apparently, at least 

 two races which lay differently sized and differently ril)bed eggs, whilst 

 the eggs of Viminia mijricae also vary very much in size. On the other 

 hand, in the Arctias and many NocTU-ii, the eggs laid are of remarkably 

 uniform size. 



c. Colour. — Eggs do not differ very much in colour when laid, 

 whitish, pale yellow or pale gi'eenish being the most usual tints, but they 

 change very quickly, and the colour of each kind j^robably then becomes 

 that which will most exactly harmonize with the surroundings amid 

 which the eggs are laid. They usually appear to make their first change 

 within 24 to 72 lioui'S of being laid. Besides this first change, almost 

 all eggs undergo a change or series of changes of colour during their 

 development ; this is generally due to the colour of the embryonic larva 

 becoming visible through the transparent egg-shell. In some species, 

 however, no change in colour takes place, notwithstanding that the egg 

 is fertile. 



The first change, however, seems to be probably due to some other 

 cause. Mr. Kobson states that " the eggs of all the species of Hepudns 

 are white, or nearly so, when first extruded, but in a very few hours 

 tliey turn to bluish-black. Mr. Hellins thinks it curious that the eggs 

 of humnli should turn black, as the young larva is white. If there was 

 anything in this remark, it would apply with equal force to all the 

 species, but the fact is, that the change of colours is of the shell only, 

 and has no connection at all with the larva within, for unim])regnated 

 eggs change in exactly the same way." This change, probably, is de- 

 pendent on the egg-contents, although it is a change of colour of the 

 shell itself, and is possibly due to the separation of the cell-contents 

 from the cell wall in the very earliest stages of change in the laid egg, 

 which probably takes place as much in an unimpregnated as in an im- 

 pregnated egg, but does not go beyond this condition in tlie former case. 

 Thus, again, the egg of Euchloe cardamines is yellow when laid, but 

 becomes deep orange in about 24 hours, and undergoes no further 

 colour-change until the larvaj hatch some days later. 



With regard to other individual species, Dr. Scudder mentions that 

 in Cercyonis alope, the colour changes from honey-yellow to pale pink ; 

 that in Eiihydryas phaeton, the original yellow becomes strongly tinged 

 with l)ro\vn, and that in Eurymus philodice, the yellow gives place to a 

 pale salmon. 



On the other hand the egg of Endromis versicolor, which is jjale 

 green when laid, rapidly becomes yellow in colour, and then, if fertile, 

 gradually changes through orange to purple, whilst the infertile egg 

 remains yellow. The first change, from green to yellow would a])pear 

 to be somewliat akin to that which takes place in E. cardamines, and is, 

 perhaps, not dependent on embryonic development ; the later changes, 

 however, are certainly due to such development. 



Dr. Jordan (E. 31. M., vii., p. 117) records the following ol)serva- 

 tion : — "The well-known chocolate-coloured egg of Centra vinida is 

 common enough ; but, at the latter end of June, 1 found an egg of 

 similar shape, only opaque white ; it was on a leaf of Salix frayilin. It 

 produced a ' puss ' genuine enough in appearance, though it unfortu- 

 nately died in early kittenhood." 



