405 



Aphides, where there is a succession of generations of imperfect 

 females, viviparously produced, derived from fertilised eggs laid in 

 the spring by perfect females, the last generation in the series 

 giving birth in the autumn to both perfect males and perfect 

 females.* True parthenogenesis is the case in which reproduction 

 is carried on for a longer or shorter time by unimpregnated females. 

 In some instances this parthenogenesis is exceptional, as in the case 

 of the silkworm-moth, only taking place under particular circum- 

 stances. In a few other Lepidpptera it " appears to be the normal 

 process." t 



It is not known within what limits parthenogenesis may continue 

 to be carried on where no access to the male can be obtained. Very 

 few experiments have been made in reference to the question. In 

 a case, however, recorded in " Nature," in which some very care- 

 fully conducted experiments were made by a Dutch entomologist 

 upon Liparis dispar, it was found that " after the first impregnation 

 of the female, in the autumn of 18G6, three successive broods of 

 caterpillars, and ultimately of moths made their appearance ; and 

 four successive times eggs were laid without further impregnation, 

 in three of which they proved endowed with vitality." As the 

 writer of this notice justly observes, the value of these experiments is 

 very great, "as bearing on the theories of spontaneous generation;" 

 and they are so easily conducted that they commend themselves to 

 all those disposed to help in caiTying on the researches which 

 science needs at the present day, — who are unable perhaps to do 

 much, but who from local circumstances can best undertake such 

 investigations as the above. X 



There is also a remarkable form of reproduction recently ascer- 

 tained to exist in certain Diptera, to which has been given the 

 name of " internal metagenesis," to distinguish it from ordinary 

 metagenesis, such as occurs in the Polypi and other low forms of 

 animal life, which propagate by budding outwards. Here the larva 



• For a full account of the nature of the process of development in the 

 Aphis, see two memoirs by Professor Huxley in Linn. Trans., vol. xxii., pp. 

 193 and 221. t Herbert Spencer, Princ. Biol., vol. i., p. 215. 



X See " Nature," vol. v., p. U9. Also vol vi., pp. 483 and 523, where a 

 detailed and interesting account is given of the latest researches on the 

 subject of " true parthenogenesis " by Siebold, who was the first to demonstrate 

 C 



