21 BRITISH LEPIDOPTEKA. 



Virgil refers to it in the Georgics, and the old authors termed the 

 phenomenon, " Lucina sine concubitu." It is now known as " aga- 

 mogenesis " or "parthenogenesis." It must be confessed that 

 scientific experiments, conducted with sufficient care, relating to this 

 subject, have been rarely performed, and that the evidence rests largely 

 on chance observations. Still, there can be no doubt that some of 

 the experiments, at least, have been sufficiently accurate to necessitate 

 a scientific explanation of the phenomenon. 



It would be out of place here to discuss the general question of 

 reproduction in the lower Invertebrates, a brief summary of which may 

 be found, Entom. Record., v., pp. 219 et seq. It need only be mentioned 

 that fission or cleavage, gemmation or budding, and encystation are 

 the more general means by which it is effected. In the Hydrozoa, 

 reproduction is carried on all the summer by gemmation, but in the 

 autumn, sperm cells and germ cells are produced in the same individual, 

 the former fertilising the latter, which then become ova, in which stage 

 these creatures pass the winter. This method of sexual reproduction 

 (i.e., with both sexes in the same individual) is very common in the 

 lower animals, but among the higher invertebrates the sexes are 

 usually differentiated in separate individuals, and, as a rule, 'coition is 

 necessary for reproduction. This is the ordinary condition among 

 insects. 



Among the Crustacea such species as Polyphemus oculus, Apus can- 

 criformis and Limnadia gigas consist, Newman says, almost entirely of 

 female individuals, the presence of a male being the exception. 

 Daphnia has males as well as females, but, according to Lubbock, the 

 females appear equally prolific in the absence of the males. Newman 

 also states that in some Arachnids the fertility of the female is not 

 dependent on coition with the male. He instances Epeira diadema, 

 which he states invariably produced fertile eggs without union with 

 a male. 



Among insects, the agamic reproduction of Aphides has long been 

 well understood. This, however, is rather different from the partheno- 

 genetic phenomenon presented by Lepidoptera, Hymenoptera, etc. In 

 the former, viviparous young are produced by the females ; in the 

 latter, eggs are laid, and produce larvae in due course, without the 

 usual intervention of the spermatozoa. 



Most of the records of the occurrence of parthenogenesis in Lepi- 

 doptera are, from a scientific point of view, most unsatisfactory, and 

 based on chance observation, rather than on specially devised experi- 

 ments. This is, perhaps, due to the fact that those entomologists who 

 inbreed insects in the largest numbers, do so in order to obtain fine 

 specimens for collections, and, as a matter of course, pair the females 

 with males in order to ensure the due fertilisation of the eggs. It 

 must also be borne in mind that, so far as our observations have gone, 

 those species that show a parthenogenetic tendency, only lay a very few 

 eggs in an occasional batch, that will produce parthenogenetic young. 

 A very large number of female motbs, therefore, would have to be 

 sacrificed in order to obtain a very small number of parthenogenetically 

 fertile eggs. This does not apply, however, to the Psychids, where 

 parthenogenesis, in some species, appears to be the rule rather than 

 the exception. 



This has been clearly shown by Jourdan in the case of Bombyx 



