21.8 FATHERLESS FROGS 



of animals), that is to say, the existence of " partheno- 

 genesis " as a natural, regularly recurring process, is excep- 

 tional. We must distinguish cases in which it regularly 

 occurs as part of the life-history of an animal or plant 

 from cases in which it has been successfully brought about 

 by experimental " artificial " methods designed by man. 

 The plant-lice " naturally " reproduce through the summer 

 by unfertilised eggs producing only females, but in the 

 first cold of autumn males are hatched from some of the 

 eggs, and the eggs of this generation are fertilised and 

 bide through the winter, hatching in the following spring. 

 Some few moths and flies also reproduce naturally during 

 summer by unfertilised eggs, and the brine-shrimps and 

 some other fresh-water shrimps produce " fatherless " 

 broods from their eggs, sometimes for years in succession, 

 until " one fine day " some males are hatched, owing to 

 what causes we do not know. The queen bee naturally 

 and regularly lays a certain number of unfertilised eggs, 

 and these produce, not females as do the unfertilised eggs 

 of plant-lice, etc., but male bees the drones and it is 

 only from such eggs that the drones of bees are born. 

 These are the chief cases of regular and natural partheno- 

 genesis, but there are others which might be enumerated. 

 On the other hand, examples of artificially induced 

 development of eggs, not fertilised, are very few. The 

 first known came accidentally to notice. Female silk-worm 

 moths reared in confinement sometimes lay eggs when 

 kept apart from the male, and these have been found to 

 hatch, and give rise to caterpillars, which were not reared 

 to maturity. Other moths bred by collectors behaved in 

 the same way, but the grubs were reared to maturity, and 

 three successive generations of " fatherless " moths were 

 obtained. In these cases the hatching of unfertilised eggs 

 is not known to occur in a state of nature, although it 

 probably occurs occasionally. It has also been observed 



