250 EVOLUTION [CHAP. IV 



Letter 176 have done so. You will please accept these papers from 

 me in token of my respect and admiration. 



As you may see from the latest of these papers, I 

 [have] recently made the remarkable discovery that there 

 [are the] so-called " three sexes ' not only in social insects 

 but [also in the] strictly solitary" genus Cynips. 



When is your great work to make its appearance? [I 

 should be] much pleased to receive a few lines from you. 



Letter 177 To B. D. Walsh. 



Down, Oct. 2 ist [1864]. 



Ill-health has prevented me from sooner thanking you 

 for your very kind letter and several memoirs. 



I have been very much pleased to see how boldly and 

 clearly you speak out on the modification of species. I 

 thank you for giving me the pages of reference ; but they 

 were superfluous, for I found so many original and profound 

 remarks that I have carefully looked through all the papers. 

 I hope that your discovery about the Cynips 1 will hold 

 good, for it is a remarkable one, and I for one have often 

 marvelled what could be the meaning of the case. I will 

 lend your paper to my neighbour Mr. Lubbock, who I 

 know is much interested in the subject. Incidentally I 

 shall profit by your remarks on galls. If you have time 

 I think a rather hopeless experiment would be worth trying ; 

 anyhow, I should have tried it had my health permitted. 

 It is to insert a minute grain of some organic substance, 

 together with the poison from bees, sand- wasps, ichneumons, 

 adders, and even alkaloid poisons into the tissues of fitting 

 plants for the chance of monstrous growths being produced. 2 



My health has long been poor, and I have lately 

 suffered from a long illness which has interrupted all work, 



1 " On Dimorphism in the hymenopterous genus Cynips," Proc. 

 Entom. Soc. Philadelphia, March, 1864. Mr. Walsh's view is that 

 Cynips quercus aciculata is a dimorphous form of Cynips q. spongifica, 

 and occurs only as a female. Cynips q. spongifica also produces spongi- 

 fica females and males from other galls at a different time of year. 



3 See Life and Letters, III., p. 346, for an account of experiments 

 attempted in this direction by Mr. Darwin in 1880. On the effects of 

 injuring plant-tissues, see Massart, " La Cicatrisation, etc.,'' in Tome 

 LVII. of the Memoires Couronnes of the Brussels Academy. 



