388 THE ENTOMOLOGIST. 



protodice larvse, but these also died before reaching the perfect 

 state. In ' Proc. South Lond. Ent. Soc' (1886, p. 32) is recorded 

 a Xanthia, supposed by Mr. South to represent X. fulvago x 

 flavago. Supposed Lyccena hellargus x corydon hybrids are re- 

 corded in the same volume (p. 61), and in * The Entomologist,' 

 1887, there is much discussion about a form of Lyccena found 

 in Kent, referred by Mr. Sabine to L. bellargus x icarus. 



With regard to this last form, which appears to occur quite 

 numerously in certain districts, the theory was proposed by Mr. 

 South that hybrids between hellargus and icarus were probably 

 fertile inter se and with the parent species, and so he supposed 

 that a local variety might have been founded directly upon the 

 results of hybridization. It is impossible to say that this could 

 not be the case; and indeed we know that by cuttings, &c., 

 florists have been able to propagate hybrids in such abundance 

 and constancy of form that they have come to be looked upon by 

 the public as genuine species, — such, for instance, is the beautiful 

 Clematis jackmanni. Nevertheless, the general laws of variation, 

 so far as we understand them, seem to point against the proba- 

 bility of the establishment in Nature of a hybrid race between 

 two forms so distinct as to be looked upon as species, because 

 when divergent varieties have become so stereotyped, their hybrids 

 are nearly always infertile, while, on the other hand, if they are 

 still plastic, the tendency of the fertile offspring ivill be more often 

 to closely resemble one or the other parent, than to take a position 

 intermediate between the two. I may have occasion to discuss 

 this question at greater length hereafter, but to enter into much 

 detail would lead rather beyond the scope of the present paper. 

 As to the cause of hybridization in Nature, it may not unfre- 

 quently be due to a scarcity of one sex of a species. For instance, 

 Hagen relates that Tetrao urogallus x tetrix hybrids occur always 

 when, by excessive hunting, the males of Urogallus (capercaillie) 

 are killed in such numbers that the females are obliged to resort 

 to the males of the other species (black grouse). In discussing 

 the Lyccena so-called hybrids, it was held by some that the fact 

 of the species not flying continuously together, but only over- 

 lapping, so to speak, was rather against the probability of 

 hybridization. To me, it seems quite the other way. 



The males of many butterflies emerge about a week before 

 the females, and for the time being must want for mates. Suppose, 

 to illustrate the point, that we have two butterflies, a and b, 

 which are double-brooded, each brood being on the wing one 

 month. The males of each species emerge a week before the 

 females, so that for the first week of the month during which the 

 species is flying we have only males, and by the fourth week the 

 males are about over, and the females largely preponderate. 

 A begins to emerge on the 1st of June, b about the 25th of the 



