ANATOMY AND PHYSIOLOGY H5 



Parthenogenesis. Reproduction without fertilization is a 

 normal phenomenon in not a few insects. This partheno- 

 genesis may easily be observed in plant lice. In these insects 

 there are many successive broods consisting of females only, 

 which bring forth living young ; at definite intervals, however, 

 and usually in autumn, males appear also, and fertilized eggs 

 are laid which last over winter. This cyclic reproduction, by 

 the way, is known as heterogeny. Among Hymenoptera, 

 parthenogenesis is prevalent, usually alternating with sexual 

 reproduction, as in many Cynipidse. In some Cynipidae, how- 

 ever, males are unknown; such is the case also in some Ten- 

 thredinidae. The statement has long been made that the un- 

 fertilized eggs of worker ants, bees and wasps produce invari- 

 ably males ; it has been found recently, however, that the par- 

 thenogenetic worker eggs of the ant Lasius niger may produce 

 normal workers ( Reichenbach, Mrs. A. B. Comstock). Males 

 may, of course, result from fertilized eggs, as in the honey bee, 

 according to Dickel, who maintains, indeed, that all the eggs 

 laid by the queen bee are fertilized. Parthenogenesis has been 

 recorded as occurring also in a few moths, some Coccidae and 

 many Thysanoptera. 



Paedogenesis. In Miastor and some species of Cecido- 

 myia, young are produced by the larva. This extraordinary 

 form of parthenogenesis is termed p&dogenesis, and is limited 



FIG. 186. 



Young paedogenetic larvae of Miastor in the body of the mother larva. Greatly en- 

 larged. After PAGENSTECHER. 



apparently to the family Cecidomyiidae. The paedogenetic 

 larvae of Miastor (Fig. 186) develop before the oviducts have 

 appeared and escape by the rupture of the mother. After 

 several successive generations of this kind the resulting larvae 

 pupate and form normal male and female flies. The pupa of 

 a species of Chironomus occasionally deposits unfertilized 

 eggs, which develop, however, in the same manner as the fer- 

 tilized eggs of the species. 



