40 The Selection Theory 



the wings? These parts have therefore degenerated because they 

 were of no further value to the insect. But if selection did not 

 influence the setting aside of these parts because they were neither of 

 advantage nor of disadvantage to the species, then the Darwinian 

 factor of selection is here confronted with a puzzle which it cannot 

 solve alone, but which at once becomes clear when germinal selection 

 is added. For the determinants of organs that have no further value 

 for the organism, must, as we have already explained, embark on 

 a gradual course of retrogi-ade development. 



In ants the degeneration has gone so far that there are no wing- 

 rudiments present in any species, as is the case with so many butter- 

 flies, flies, and locusts, but in the larvae the imaginal discs of the 

 wings are still laid dovm. With regard to the ovaries, degenera- 

 tion has reached difierent levels in different species of ants, as has 

 been shown by the researches of my former pupil, Elizabeth Bickford. 

 In many species there are twelve ovarian tubes, and they decrease 

 from that number to one ; indeed, in one species no ovarian tube at 

 all is present. So much at least is certain from what has been said, 

 that in this case everything depends on the fluctuations of the 

 elements of the germ-plasm. Germinal selection, here as elsewhere, 

 presents the variations of the determinants, and personal selection 

 favours or rejects these, or, — if it be a question of organs which have 

 become useless, — it does not come into play at all, and allows the 

 descending variation free course. 



It is obvious that even the problem of coadaptation in sterile 

 animals can thus be satisfactorily explained. If the determinants 

 are oscillating upwards and downwards in continual fluctuation, and 

 varying more pronouncedly now in one direction now in the other, 

 useful variations of every determinant will continually present them- 

 selves anew, and may, in the course of generations, be combined with 

 one another in various ways. But there is one character of the 

 determinants that greatly facilitates this complex process of selection, 

 that, after a certain limit has been reached, they go on varying in 

 the same direction. From this it follows that development along 

 a path once struck out may proceed without the continual interven- 

 tion of personal selection. This factor only operates, so to speak, at 

 the beginning, when it selects the determinants which are varying in 

 the right direction, and again at the end, when it is necessary to put 

 a check upon further variation. In addition to this, enormously long 

 {)eriod8 have been available for all these adaptations, as the very 

 grarlual transition stages between females and workers in many species 

 plainly show, and thus this process of transformation loses the 

 marvellous and mysterious character that seemed at the first glance 

 to invest it, and takes rank, without any straining, among the other 



