16 BRITISH LEPIDOPTERA. 



the larvae, viz., A. fasciata, 23 ' per cent.; D. abietis, 12 per cent.; 

 0. pruni, 64 per cent. ; D. pini, 28 per cent. 



It has been suggested that the sex of the imagines reared from eggs 

 can be determined by the conditions in regard to abundance of food, 

 or the reverse, under which the larvae are reared ; that, under a 

 specially nutritious diet, lepidopterous larvae tend to produce female 

 imagines, whilst a starvation diet tends to the production of males. 

 This, of course, assumes a neutral condition as regards sex in the 

 newly-hatched larva, but the experiments that are supposed to have 

 proved this simply show that male larvae will stand more starving than 

 those of females, or, in other words, that the minimum food which 

 will allow male larvae to just pupate, is, in the same species, often 

 insufficient to allow the process in female larvae, which die under 

 such extreme treatment. The sexual organs of newly-hatched larvae 

 are moderately well-developed. 



Another theory which has been assumed, viz., that eggs laid suc- 

 cessively by the same female are of opposite sex, has been entirely 

 disproved, and experiment has shown that the relative proportion of the 

 sexes is subject to immense fluctuation on the separate dates on 

 which eggs are laid. As regards eggs laid on any one day, the 

 sexes generally succeed each other in little groups of irregular size. 

 It is further recorded that the pupae obtained from different batches of 

 Vanessa to had a large proportion of a certain sex, some batches pro- 

 ducing almost entirely males, others consisting almost entirely of 

 females. 



The eggs of Lepidoptera are developed in the ovaries of the parent, 

 whence they pass down the oviduct into the vagina. In connection 

 Avith the vagina are one or more pouches called receptacula seminis, 

 in which the spermatozoa are stored after copulation. As the egg 

 passes along the vagina to the ovipositor, the spermatozoa, or sperm- 

 cells, are released from the receptacula, and certain of them enter the 

 egg through the micropylar tubes, one of which fertilises the egg. 

 Fertilisation, then, takes place at the time that the egg is being laid, 

 by the spermatozoa entering the micropylar pores at the time that the 

 egg passes the pouches. It is sometimes noticed that the latest-laid 

 eggs of a moth are infertile, a result probably due to the supply of 

 spermatozoa being exhausted before all the eggs are laid. It is well- 

 known that many Lepidoptera pair more than once. Anticlea ber- 

 berata, Tephrosia bistortata, and various Zygaenid species have been 

 observed to do so repeatedly. No doubt, the habit is of common 

 occurrence. 



CHAPTER III. 



EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. 



It may be well now to briefly consider the changes that take place 

 in the fertilised ovum or egg, and that have, as their result, the pro- 

 duction of an individual resembling its parents. These changes are 

 of the utmost importance, and the embryological studies made by 

 various entomologists have done much to throw light upon the wider 

 biological problems which embryology presents. 



