698 



SCIENCE. 



[N. S. Vol. XXIV. No. 622. 



namely, that the drones of worker parentage 

 show a much larger variation than those of 

 queen parentage. Their coefficient of varia- 

 tion is from 50 per cent, to Y5 per cent, greater. 

 Also if results d and c are to be accepted with 

 reservations, then so are the interpretations of 

 their significance. 



It may be said by some that the larger vari- 

 ation in the drones as compared with the vari- 

 ation in the workers may be due to the 

 fact ( ?) that ' males vary more than females.' 

 This generalization, which is one of Darwin's 

 variation canons, has long been disproved as 

 a general law. It is true in certain cases or 

 classes of cases, these being mostly those in 

 which the males possess certain secondary 

 sexual characters of ornament and bizarrie, 

 such as tufts, plumes, horns, processes, etc. 

 The variation in such characters seems to be 

 larger than in other body parts or at least 

 this is generally believed to be true, although 

 I do not now recall the detailed variation 

 studies on which this belief is based, or should 

 be based. But the characters chosen for study 

 in the bees are precisely such as are not sec- 

 ondary sexual ones or special adaptations but 

 are characters common in structure and use 

 to both drones and workers. In other varia- 

 tion studies of exactly these characters, name- 

 ly, characters of wing venation, in other kinds 

 of insects, for example, the mosquito, we have 

 not found the males to show a larger variation 

 than the females. In these other cases both 

 sexes are of bi-sexual parentage. 



Variation in female aphids (parthenogenet- 

 ically produced). — In the following paragraphs 

 is presented a brief statement of the variation 

 conditions found to exist in the venation of a 

 series of parthenogenetically produced female 

 insects. Unfortunately, the variation of these 

 parthenogenetically produced females can not 

 be compared with that in series of bi-sexual 

 parentage of either sex in the same species, 

 but, thanks to the methods of the biometri- 

 cians, the mathematical expression of this 

 variation (the coefficient of variation accord- 

 ing to Pearson's formula) allows us to com- 

 pare its extent with the variation of venation 



characteristics in other kinds of insects, male 

 or female, of bi-sexual parentage. 



In a series of 200 winged females of the 

 mustard plant louse (species unknown), pro- 

 duced viviparously by agamic stem-mothers, 

 and collected on the university campus, the 

 variation in wing size, in dimensions of vein- 

 parts, in modification of the venation (addi- 

 tion or loss of branches and cells, etc.) in fore 

 and hind wings, and the number of grasping 

 hooks on the hind wings were studied. In all 

 these characters a notable variation is ap- 

 parent. In modification of venation (addi- 

 tion or loss of branches, change of forking, 

 interpolated cells and the like), 76 wings out 

 of the 800 show notable variation. No bio- 

 metric expression can, of course, be given for 

 this substantive variation. For the meristic 

 variation, however, in number of costal hooks, 

 in length and breadth of wings, in length of 

 various vein-parts (varying independently of 

 the varying size of the wings) the coefficients 

 of variation have been determined, and are 

 notably large. For example, they are a§ large 

 as the coefficients of the variation in similar 

 wing-parts in mosquitoes,^ ants and worker 

 bees, in all of which amphimixis is the rule. 

 We have not been able to compare the varia- 

 tion in parthenogenetically produced aphids 

 with that in the early spring generation of 

 stem-mothers that comes from eggs of bi- 

 sexual parentage. Perhaps we shall be able 

 to do this in another year. But what we have 

 already before our eyes is sufficient to show 

 us that variation actually exists among these 

 parthenogenetic individuals in extent and 

 character sufficient to serve natural selection 

 as a species-building basis, if the familiar 

 fluctuating, continuous or Darwinian variation 

 ever is sufficient for this purpose. Amphi- 

 mixis is not only not necessary in order to 

 insure Darwinian variation, but there is no 

 evidence (that I am aware of) to show that it 

 increases this variation. There is, on the 

 other hand, a little evidence, some of it pre- 



' For determinations of variation conditions in 

 these other insects see Kellogg and Bell, ' Studies 

 of Variation in Insects,' Proc. Wash. Acad. Sci., 

 Vol. 6, pp. 203-332, 1904. 



