90 THE EVOLUTION THEORY 



do not oven dovolop in tlio pupa'; they are, as Dowitz showed, 

 present even now in the lurva in the Form oi' iniaginal disks, but 

 from the pupa-stage onwards they degenerate, and the segments 

 of the thorax to wliich tliey are attached likewise appear small and 

 modified. A variation of the germ-plasm miist therefore have taken 

 place, and to this is due the fact that the wing-primordia no longer 

 develop, and that the thorax has a different development from what 

 it had at the time when the animals were still fertile. 



It has indeed been said that there is no need for assuming 

 a variation of the germ-plasm, since the degeneration of the wing 

 might be produced by inferior noxirishment. This opinion is based 

 on the fact that, among bees, the workers do actually arise from 

 female larvse which have reciuved a meagre diet poor in nitrogenous 

 elements, while the wame female larvas supplied with an abundant 

 diet rich in nitrogen develop into (pieeiis. 



But even though we may assume that there is a similar dili'eri'nce 

 in the mode of feeding among most ants, because the workers are 

 considerably smaller than the fertile females, it would be quite 

 erroneous to conclude that the diH'erence between the two types 

 rests solely ox\ the effect of differences in diet. The elinunation 

 of an individual organ has never yet been determined by bad and 

 scanty nourishment ; it is tht^ whole animal with all its parts that 

 degenerates and becomes small and weakly. Often as catei'pillars 

 of different species have been placed on starvation diet, whether 

 for experimental purposes or to proeun', very small butterflies, it 

 has never yet happentMl that a single organ, .such as antenna, leg, 

 or wing, has thereby been eliminated or caused to degenerate. I have 

 myself instituted many such expciriments with the maggots of the 

 blue-bottle fly, by supplying them from their earliest youth with just 

 as little food as possible without actually stai-ving them to death, yet 

 never have these larvai given rise to flies in which the wings were 

 absent or rudimentary. 



Nor did these starved flies t^ver exhibit degenerate ovaries ; 

 they werc! always completely devoloj)ed and equi]>p(Ml with the 

 full number of ovarian-tubi^s. It was to decide this particular point 

 that these experiments wei'c instituted, for my opponents maintained 

 that degeneration of tlui ovaries was a direct result of inferior 

 nourishment. But tliat is not the case. Special investigations in 

 regard to ants, undertakiiu at my request by Miss Pjli/.abeth Bickford, 

 showed that the anatomical i-esults reached by earlier investigators, 

 like Adlerz and Lespfes, in regard to the degeneration of the ovaries 

 in workers, were absolutely correct, and that the ' degenera-tion ' 



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