HYMENOPTERA. 13 



liberty, feeding on the foliage of trees ; the latter are free, so far as they are not 



confined within an egg-membrane, but being internal feeders, whether in foliage 



larvae, wood, or shut up as solitary hermits, each in its several cell passes a larval 



period of limited freedom. It is a curious fact that the legs of some larvae are 



more evident in an early than in the latter stages, thus proving that the habit of 



cell-life is a comparatively recent departure from a former habit, when in all 



probability the larval life was passed in greater freedom. 



The phenomenon of parthenogenesis is one which crops up in 

 Development. . , . . . 



various orders of insects, being simply the production by the female 



of eggs or young without the fertilisation of the egg-germs within the female, by 

 the stimulative elements necessary to the production of young in the higher 

 animals. It is not, however, a chance phenomenon, appearing as a race-preserving 

 expedient, on the sudden failure of male forms, but one of nature's resources for 

 preserving the continuity of species. It is constant in many species of the 

 Hymenoptera, in the form of what is known as the alternation of generations ; in 

 some species, however, it is supposed to be the sole form of reproduction, for the 

 males of these species have never yet been discovered. Whether we regard 

 the fertilisation of the female egg-germs by the male elements as dynamic or 

 stimulative, or as merely a matter of the interchange of character determinants 

 between the two sexes, it appears to be beyond a doubt that a continuous 

 succession of virgin-reproductions must inevitably tend to the degeneration and 

 ultimate extinction of the race. Parthenogenesis or virgin-reproduction may 

 be of three kinds. First, resulting in the production of the male sex only ; 

 second, of the female alone ; and thirdly, in cases when the young are produced 

 not as eggs in the first instance, but alive, as in the case of the plant-lice or 

 Aphidce. It seems that parthenogenesis does not favour the production of one 

 sex more than another. We should, therefore, be cautious how we accept too 

 hastily the commonly received belief that male bees are necessarily the offspring 

 of non-fertilised eggs. It by no means follow^ that because an egg was not 

 fertilised that therefore the sex produced in it is the direct result of non- 

 fertilisation. The question, however, is still a matter of controversy, and more 

 evidence is needed before final conclusions can be reached. 



That the members of this order are on the whole useful to man cannot be 

 doubted, — more useful perhaps than the majority of insect forms, — whether as bees, 

 with their honey-storing instincts, or as the ichneumon tribes dealing destruction 

 to thousands of the larvae — those insect pests which would otherwise work terrible 

 havoc with our corn crops and garden produce. On the other hand, it must be 

 confessed that the larvae of the saw-flies often work damage to the foliage of 

 forest-trees, while in many tropical climates ants are a devouring scourge to all 

 that belongs to man. 



We must now leave these introductory lines, but before passing 

 Classification. , ,,.,,, . ,. „ . . . , ., . 



on to a more or less detailed description of certain species and their 



peculiar characteristics of structure and of habit, the subjoined outline of classifica- 

 tion of the various families of the order will give a general idea of the different 

 groups, which are more obviously separated by certain broad distinguishing 

 characters. 



