126 THE BIOLOGICAL PROBLEM OF TO-DAY 



are of two kinds, known as workers and soldiers. 

 The divergences of structure among the three or 

 four forms are shown, frequently by considerable 

 differences in size, by the presence and absence of 

 wings, by differences in the sense-organs, the brain, 

 and the structure of the head. In the common 

 ant Solenopsis fugax, for instance, as Weismann 

 quotes from Forel the males have more than 

 four hundred facets on their eyes, the females 

 about two hundred, and the workers from six to 

 nine. Many soldiers possess enormously large and 

 heavy heads, with massive jaws, and naturally, 

 with the appropriate muscles much enlarged. 



But as workers and soldiers, on account of the 

 rudimentary state of their sexual organs, cannot 

 reproduce themselves, all the three or four kinds 

 of ants in the colony must be developed from eggs 

 deposited by the females. In this Weismann finds 

 the most convincing proof of the omnipotence of 

 natural selection, and, I venture to add, for the 

 omnipotence of his doctrine of determinants. 



He says (Contemporary Review, vol. Ixiv., 

 p. 313) : ' It fortunately happens that there are 

 animal forms which do not reproduce themselves, 

 but are always propagated anew by parents which 

 are unlike them. These animals, which thus 

 cannot transmit anything, have nevertheless varied 

 in the past, have suffered the loss of parts that 

 were useless, and have increased and altered 

 others ; and the metamorphoses have at times 

 been very important, demanding the variation of 

 many parts of the body, inasmuch as many parts 



