INTRODUCTION 23 



fertilised eggs while still a pupa. These eggs pro- 

 duced larvae. The egg-laying pupa had on the under 

 side of the last abdominal segment a pair of special 

 orifices for the passage of the eggs. Occasionally, 

 after laying a few eggs, the pupa was transformed 

 into a fly. In autumn the normal stages were gone 

 through, and eggs were laid by winged females after 

 being fertilised by the males. Many other cases are 

 known of the production of fertile though unfertilised 

 eggs (Parthenogenesis) among Insects and other 

 animals. Reproduction by immature animals (Paedo- 

 genesis), as in Grimm's Chironomus, is rare but not 

 unparalleled. The larva of a minute fly (Miastor 

 metroloas) found under the bark of the poplar, willow 

 and beech, was observed to produce viviparously 

 small larvae, which escaped by tearing open the body 

 of their parent and in turn produced other larvae after 

 the same fashion. This went on throughout the 

 greater part of the year, but in summer winged males 

 and females appeared, which laid a very few eggs of 

 large size. When these facts were first published by 

 Wagner ^ they were received with a good deal of 

 incredulity, which has been completely removed by 

 the independent verification of the facts, and by the 

 discovery of two other allied species of similar life- 

 history. Parthenogenesis, Paedogenesis and viviparous 

 reproduction are all methods of abridging the tedious 

 operations by which in Insects a new generation is 

 normally produced. Where food is plentiful and 

 time precious, the mating of the sexes, the full 



^ "Beitr. z. Lehre v. d. Fortpflanzung der Insectenlarven," 

 Zeits.f. wiss. Zool. Bd. XIII. p. 513 (1863). 



