658 APPENDIX B. 



Ip.y eggs these produce drones only.* Special evidence, harmon- 

 izing with general evidence, thus proves that among the social 

 insects the sex is determined by degree of nutrition while the egg 

 is being formed. See then how congruous this evidence is with 

 the conclusion above drawn ; for it is proved that after an egg, 

 predetermined as a female, has been laid, the character of the 

 produced insect as a perfect female or imperfect female is deter- 

 mined by the nutrition of the larva. That is, one set of differences 

 in structures and instincts is determined hy nutrition before the egg 

 is laid, and a further set of differences in structures and instincts is 

 determined hy nutrition after the egg is laid. 



We come now to the extreme case — that of the ants. Is it 

 not probable that the process of differentiation has been similar ? 

 There are sundry reasons for thinking so. With ants as with 

 wasps and bees — the workers occasionally lay eggs ; and an ant- 

 community can, like a bee-community, when need be, produce 

 queens out of worker-larvae : presumably in the same manner by 

 extra feeding. But here w^e have to add special evidence of great 

 significance. For observe that the very facts concerning ants, 

 which Professor Weismann names as exemplifying the formation 

 of the worker type by selection, serve, as in the case of wasps, to 

 exemplify its formation by arrested nutrition. He says that in 

 several species the egg-tubes in the ovaries show progressive 

 decrease in number ; and this, like the different degrees of arrest 

 in the ovaries of the worker-wasps, indicates arrest of larva- 

 feeding at different stages. He gives cases showing that, in 

 different degrees, the eyes of workers are less developed in the 

 number of their facets than those of the perfect insects ; and 

 he also refers to the wings of workers as not being developed : 

 remarking, however, that the rudiments of their wings show that 

 the ancestral forms had wings. Are not these traits also results 

 of arrested nutrition ? Generally among insects the larvae are 

 cither blind or have but rudimentary eyes ; that is to say, visual 

 organs are among the latest organs to arise in the genesis of 

 the perfect organism. Hence early arrest of nutrition will stop 

 formation of these, while various more ancient structures have 

 become tolerably complete. Similarly with wings. Wings are 

 late organs in insect phylogeny, and therefore will be among 

 those most likely to abort where development is prematurely 

 arrested. And both these traits will, for the same reason, natu- 

 rally go along with arrested development of the reproductive 

 system. Even more significant, however, is some evidence as- 

 signed by Mr. Darwin respecting the caste-gradations among the 

 driver ants of West Africa. He says : — 



* Natural History of Bees, new ed., p. 33. 



