ON THE VARIATION OF INSECTS. 



237 



white surroundings produced white and very light yellow cocoons. 

 A larva which spun a white cocoon had previously commenced a 

 brown one, but on being removed to white surroundings it pro- 

 duced white silk. Mr. G. F. Mathew has recorded some very 

 interesting experiments (Trans. Ent. Soc. Lond. 1885, 364), 

 showing the influence of surroundings on the pupsB of species of 

 Papilio. P. godeffroyi, which had been allowed to pupate on 

 scarlet or white paper, gave rosy-pink pupa?, while those on blue 

 or yellow paper were green, and those on black paper very dark 

 green. P. schmeltzi was also experimented upon, but was not so 

 much affected by the colour of background : this was attributed 

 to its having a thicker pupa-shell. The newly-changed pupae of 

 both species were pale green, and it was not until several hours 

 had elapsed that they assumed the colour produced by their 

 surroundings. Mr. Mathew ventures an explanation of these 

 curious phenomena, and says " They are very soft, and are covered 

 with a thin coathig of some viscid substance, which may have 

 the power of absorbing refracted rays of colour-light as they dry 

 and harden." This, however, is rather a peculiar hypothesis, 

 since, if the pupse were to " absorb " the light reaching them and 

 refracted from the coloured paper, it is to be presumed that they 

 would not at the same time reflect it, and their colour would 

 consequently be the complementary one to that of their sur- 

 roundings, or more probably black. 



Hybrids. 



The frequency and probability of hybri ;s in Nature has been 

 very freely discussed at different times, but, owing to the difficulty 

 of obtaining satisfactory data, without any very decisive result. 

 Yet it is quite certain that, at any rate under artificial conditions, 

 hybrids may occur both among plants and animals between genera 

 that are universally considered distinct, while hybrids between 

 allied species are frequently found in Nature. The ducks among 

 birds, and the willows, thistles, and verbascums among plants, 

 afford excellent instances. This being so, there is no apparent 

 reason why hybrid insects should not also occur under natural 

 circumstances, and, as a matter of fact, many such have been 

 recorded. Hagen (Canad. Ent. 1876, 78) enumerates the fol- 

 lowing hybrids which he found recorded in European literature : 

 — Saturnia carpini x spini (larva), " Sphinx " vespertilio x 

 euphorhicB (larva), ''Sphinx'' vespertilio x hippophaes (larvii), 

 "Sphinx" euphorhice x galii (imagines, near Berlin), Zycjceiia 

 trifolii X filipendulce (imago, England), Colias edusa x hyale, 

 LyccBua adonis x alexis, Hipparchia arcania x hero, Cceno- 

 nympha pamphilus x iphis, Vanessa urticce x atalanta. A. Wailly 

 (Canad. Ent. 1880, 228) had hybrid larvae of Samia ceanothi x 

 gloveri, but they died. P. II. Hoy obtained hybrid Pieris rapce x 



