192 AN INTRODUCTION TO ENTOMOLOGY 



Some writers make use of the term ovoviviparous indicating the production 

 of eggs that have a well -developed shell or covering, but which hatch within the 

 body of the parent; but the distinction is not fundamental, since viviparous ani- 

 mals also produce eggs as indicated above. 



Among viviparous insects there are found every gradation from 

 those in which the larvae are born when very young to those in which 

 the entire lar\^al Hfe is passed within the body of the parent. There 

 also exist examples of viviparous larvae, viviparous pupae, and vivi- 

 parous adults. And still another distinction can be made; in some 

 viviparous insects the reproduction is parthenogenetic ; in others it 

 is sexual. 



Viviparity with parthenogenetic reproduction. — In certain vivipar- 

 ous insects the reproduction is parthenogenetic; that is, the young are 

 produced from eggs that are not fertilized. This type of reproduction 

 occurs in larv^ae, pupse, and apparently in adults. 



Padogenetic LarvcB. — In 1862 Nicholas Wagner made the remark- 

 able discovery that certain larvag belonging to the Cecidomyiidas give 

 birth to living young. This discovery has been confirmed by other 

 observers, and for this type of reproduction the term pcedo genesis, 

 proposed by Von Baer, has come into general use. This term is also 

 spelled pedogenesis; the word is from pcedo or pedo, a child, and genesis. 



The phenomenon of paedogenesis is discussed later in the accounts 

 of the Cecidomyiidse and of the Micromalthidse. 



Pcedogenetic pupcE. — The most frequently observed examples of 

 paedogenetic reproduction are by larvas; but that pupas also are some- 

 times capable of reproduction is shown by the fact that Grimm ('70) 

 found that eggs laid by a pupa of Chironomus gtimmii, and of course 

 not fertilized, hatched. 



Anton Schneider ('85) found that the adults of this same species of 

 Chironomus reproduced parthenogenetically. This species, therefore, 

 exhibits a transition from paedogenesis to normal parthenogenesis. 



Viviparous adult agamic females. — There may be classed under this 

 class provisionally, the agamic females of the Aphididae ; as these are 

 commonly regarded as adults. It has been suggested, however, that 

 the agamic reproduction of the Aphids may be a kind of paedogenesis ; 

 the agamic females being looked upon as nymphs. This however, is 

 not so evident in the case of the winged agamic generation. On the 

 other hand, the reproductive organs of the agamic aphids are incom- 

 pletely developed, as compared with those of the sexual forms, lacking 

 a spermatheca and colleterial glands. 



