388 LECTURE XVIII. 



parts of generation assume in some species of insects. But all insects 

 are dioecious, or of distinct sex : and there are not only " males " and 

 "females;" but in certain families there are other kinds of indivi- 

 duals, which are essential to the successful propagation of the species. 

 In the social Bees and Ants, for example, there is a third form or con- 

 dition of the individual, commonly called "neuter," and sometimes 

 labourer or nurse : these, however, are essentially female, having the 

 female organs, but imperfectly developed and passive. The working 

 bee, at least, exercises the function of only one part of those organs, 

 an accessory part, which is metamorphosed into a special poison 

 organ, but which is the homologue of the ovipositor in fertile female 

 insects. This working bee, or " non-breeder/' as Hunter called her, 

 relieves the parturient queen of her ova, places them in the appro- 

 priate nest-cell, and feeds the larva when it is hatched : it thus acts 

 the part of midwife as well as nurse, and is an indispensable adjunct 

 to the nmltiplication of the species. There is, again, in insects^ a 

 fourth modification of the individual, in relation to the sexual func- 

 tion. I allude to that remarkable state of the Aphis, which, like the 

 working bee, is an arrested stage of the female, constituting the larvi- 

 parous individual, but which propagates by a kind of internal gem- 

 mation, without sexual concourse in her own person. She possesses, 

 however, the female organs ; but, contrariwise to the working bee, 

 the external and accessory parts of the apparatus are wanting, 

 whilst the more essential organs are extremely active. Thus, at the 

 outset of our survey of the generative system and function in 

 hexapod insects, we encounter four different kinds of individuals in 

 relation to that function — males, nubile females, sterile females, and 

 procreant virgins. 



Certain modifications of the generative functions have served as a 

 basis for the classification of the hexapod insects, some of which, as 

 e. g. Aptera, are said to undergo no metamorphosis, and have been 

 called "ametabola." Others, as e.g., the Myriapoda, Hemiptera, 

 and Ortlioptertty are described in entomological treatises as undergoing 

 only a partial metamorphosis, and are called, " hemimetabola." The 

 metamorphosis being more patent and conspicuous in the rest of 

 the class, is admitted, said to be perfect or complete, and made the 

 characteristic of the "metabola." The divisions so founded and de- 

 fined are insufficient, however, for the generalizations of the compara- 

 tive anatomist, and, by that very defect, are evidently less natural 

 than the orders in the Linnaean system, from the characters of the 

 wings. 



The external characters which distinguish the sexes of insects 

 are least conspicuous in the Myriapoda: the external outlets of 



