HYMENOPTERA 497 



but there is no communication between the stomach and the 

 posterior intestine. 



Packard informs us ^ that in Bomhus the larva, after it is 

 full fed, passes into the pupa state (Fig. 331, A, B) by a 

 series of transformations accompanied by moultings of the skin. 

 Packard's statements have been confirmed by others, but details 

 have not been fully given, so that the number of the moults, 

 their intervals and other particulars, are still unknown. We 

 have remarked that the pupal instar is very like the perfect instar, 

 except that it is colourless and soft, and that each of the members 

 is wrapped in a very delicate skin ; the colour appears gradually. 

 This metamorpliosis exhibits important differences from that of 

 the Lepidoptera. Packard calls tlie Insect, during the stages of 

 transformation from the full-fed larva to the pupa, the semi-pupa ; 

 the later stages of the pupa, when the colouring has appeared, he 

 terms the subimago. Altogether he considers there is a series of 

 at least ten moultings of the skin. His ideas were apparently 

 derived from examination of a series of specimens after death 

 rather than from observation of the development in living indi- 

 viduals. The parasitic forms of Hymenoptera have apparently 

 extraordinary metamorphoses of very varied kinds. 



Parthenogenesis. One of the most remarkable facts con- 

 nected with this Order is the prevalence of parthenogenesis in a 

 considerable number of widely separated species. In many of 

 these Hymenoptera it is not a mere occasional occurrence, but 

 plays an important part in the continuity of the species ; in- 

 deed, it is believed that in some members of the Order the 

 reproduction is entirely parthenogenetic. We shall give par- 

 ticulars as to some of these cases in subsequent chapters, and 

 will here make some remarks on the different forms of partheno- 

 genesis existing in the Order. The three forms of parthenogenesis 

 mentioned on p. 141 all occur in Hymenoptera. In the gall- 

 making Cynipidae parthenogenesis is frequently accompanied with 

 alternation of generations, a generation consisting of the two sexes 

 being followed by another consisting entirely of females, wdiich 

 in its turn gives origin to a bisexual generation. In this case 

 deuterotokous parthenogenesis is established as a part of the normal 

 economy of the species. This same form of parthenogenesis also 

 occurs in other species of Cynipidae unaccompanied by alternation 



1 P. Boston Soc. X. 1866, p. 279. 

 VOL. V 2 K 



