270 CAUSES OF VARIATION 



Insect poisons. The poison of bees formic acid is fata] 

 to insects and small animals, and in sufficient quantity to the 

 larger vertebrates, including man, though frequent stings of a 

 moderate number lead rapidly to acclimatization. It is note- 

 worthy, too, in this connection that the sting of the insect 

 (mud wasp, for example) does not always kill but often merely 

 paralyzes, so that the creature stored with the egg will remain 

 alive to furnish food to the larvae some weeks later. 



Galls. Galls are the direct result of the sting of an insect, 

 leaving a specific poison to act upon a particular form of proto- 

 plasm. The result is not death but a diverting of the activities 

 into entirely new channels. Darwin states that " no less than 

 fifty-eight kinds of gall are produced on the several species of 

 oaks by Cynips with its sub-genera, and Mr. B. D. Walsh states 

 that he can add many more." l 



Darwin further remarks that many gall insects are exceedingly 

 small, and that consequently the drop of poison they inject must 

 be exceedingly minute ; moreover, it is never injected but once. 

 The growth that follows, however, is specific and continuous. 

 He quotes Walsh as saying, " Galls afford good, constant, and 

 definite characters, each kind keeping as true to form as does 

 any independent organic being," 2 and he calls our attention to 

 the fact that seven of the ten distinctly different galls produced 

 on the willow are by insects which, " though essentially distinct 

 species, yet resemble one another so closely that in almost all 

 cases it is difficult and in most cases impossible to distinguish 

 the full-grown insects one from another." The difference in the 

 quality of the poison secreted by insects so nearly alike cannot be 

 great, yet it is sufficient to give rise to galls widely different. 

 Last, and not least, he mentions that " Cynips fecundatrix has 

 been known to produce in the Turkish oak, to which it is not 

 properly attached, exactly the same kind of gall as on the 

 European oak. These latter facts apparently prove that the 

 nature of the poison is a more powerful agent in determining 

 the form of the gall than [is] the specific character of the tree 

 which is acted on."* 



1 Darwin, Animals and Plants, II, 272. 2 Ibid. p. 273. 



a We know now that the gall does not develop unless the egg hatches. 



