PARTHENOGENESIS. 41 



The pupae of different insects vary greatly in form. In 

 the insects with an incomplete metamorphosis the pupa 

 only differs from the larva in having pad-like rudimentary 

 wings. In such insects development is direct, and properly 

 speaking they pass through no true larval or pupal stages. 

 Indeed, some authors with good reason apply the term 

 ni/mph to the early stages of Orthoptera, white ants, may- 

 flies, dragon-flies, etc.; this term embracing what is usually 

 called the larval and pupal states of those insects, as during 

 these periods they are active and take food. 



The Imago. This is the final or adult state, when the 

 wings are developed and the insect is able to fly about 

 and lay its eggs. As soon as insects, such as moths or 

 butterflies, wasps or bees, have completed their transforma- 

 tions they pair, and the females seek a suitable place to 

 deposit their eggs. After this act is accomplished, the 

 adults usually soon die. This period of reproduction may 

 occur at any time during the summer, but, taking into 

 account the great mass of species, it in general occurs to- 

 ward the end of summer, and early in the autumn; hence 

 during the winter the species in most cases is represented 

 by the egg alone. Earely does the adult insect hibernate; 

 though one will find a few ichneumons, beetles, and bugs 

 under leaves and the bark of trees; but in many species, 

 especially moths, the pupa hibernates to disclose the imago 

 in the spring or early summer. Larvae seldom live through 

 the winter, although there are some well-known exceptions 

 to this law. 



When insects are prevented from mating, they will live 

 much longer than would be otherwise the case. Reaumur 

 kept a virgin butterfly for two years in his hot-house. The 

 pupal state of moths and butterflies may be greatly pro- 

 longed by keeping the chrysalids on ice. 



Parthenogenesis. Besides the normal mode of develop- 

 ment, certain insects, as the plant-louse (ApJiis), the bark- 

 louse (Coccus), the honey-bee, the Polistes wasp, the currant 

 saw-fly (Nematus), the gall-flies, and a few others, prc- 



