462 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



structures and habits and social instincts can take 

 place independently of use-inheritance. The wonder- 

 ful instincts of the working-bees have apparently been 

 evolved (at least in all their later social complications 

 and developments) without the aid of use-inheritance- 

 nay, in spite of its utmost opposition. Working-bees, 

 being infertile 'neuters,' cannot, as a rule, transmit 

 their own modifications and habits. They are de- 

 scended from countless generations of queen-bees and 

 drones, whose habits have been widely different from 

 those of the workers, and whose structures are dissim- 

 ilar in various respects. In many species of ants there 

 are two, and in the leaf-cutting ants of Brazil there 

 are three, kinds of neuters which differ from each other 

 and from their male and female ancestors 'to an al- 

 most incredible degree.' 1 The soldier caste is distin- 

 guished from the workers by enormously large heads, 

 very powerful mandibles, and extraordinarily different 

 instincts. In the driver ant of West Africa one kind 

 of neuter is three times the size of the other, and has 

 jaws nearly five times as long. In another case, 'the 

 workers of one caste alone carry a wonderful sort of 

 shield on their heads.' One of the three neuter classes 

 in the leaf-cutting ants has a single eye in the midst of 

 its forehead. In certain Mexican and Australian ants 



1 Origin of Species, pp. 230-232 ; Bates' s Naturalist an the Amazons. Dar- 

 win is surprised that no one has hitherto advanced the demonstrative case of 

 neuter insects against the well-known doctrine of inherited habit as advanced 

 by Lamarck. As he justly remarks, "it proves that with animals, as with 

 plants, any amount of modification may be effected by the accumulation of 

 numerous slight, spontaneous variations, which are in any way profitable, 

 L without exercise or habit having been brought into play. For peculiar habits^ 

 confined to workers, however long they might be followed, could not possibly 

 affect the males and fertile females, which alone leave any descendants." 

 Some slight modification of these remarks, however, may possibly be needed 



I to meet the case of " factitious queens," who (probably through eating par- 

 ticles of the royal food) become capable of producing a few male eggs, 



