MANIFESTED IN THE ANIMAL KINGDOM 93 



of worker bees is not due to the law which governs the 

 union of aperm cell and ovum, but that there appears 

 to be a complete failure of the sexual instinct and of 

 ovulation. 



Ants exhibit the same phenomena as bees. The 

 sterile workers are among the most remarkable examples 

 of cerebral development in the insect world, and Darwin 

 considered the brain of an ant to be the most wonderful 

 speck of matter in the world. The fertile females show 

 the same intellectual deficiency as the queen bee. The 

 female of the white ant loses even the power of locomotion, 

 grows to an enormous size, and becomes a mere egg- 

 producing machine. 



In his Variation of Animals and Plants under Domestica- 

 tion Darwin provides a mass of evidence bearing on the 

 problem of fertility. The first impression produced on 

 examining this evidence is one of hopeless confusion. 

 The facts appear to be a mass of contradictions and to 

 conform to no law. When, however, we apply the 

 principle of the vital optimum and get the abstract 

 principles straightened out the facts fall readily into line. 

 It is a necessary deduction from the theory of organic 

 evolution that the animal and vegetable kingdoms are 

 governed by the same general biological laws, and 

 the facts in the two cases are exactly parallel. Plants 

 are rendered sterile both by excessively favourable and 

 by excessively unfavourable conditions, and the same 

 is true of animals. Plants are apt to be rendered less 

 fertile when first transplanted into the more favourable 

 conditions of cultivated gardens, and wild animals are 

 rendered less fertile when first confined and highly fed. 

 Plants may have their fertility greatly increased by 

 selection, and the same is true of animals. Both may 

 be adapted to develop a high degree of fertility under 



