Degeneration of disused parts 39 



change. Nor do we know how far a determinant must be strengthened 

 by the passive flow of the nutritive stream if it is to be beyond the 

 danger of unfavourable variations, or how far it must be weakened 

 passively before it loses the power of recovering itself by its own 

 strength. It is no more possible to bring forward actual proofs in 

 this case than it was in regard to the selection-value of the initial 

 stages of an adaptation. But if we consider that all heritable varia- 

 tions must have their roots in the germ-plasm, and further, that when 

 personal selection does not intervene, that is to say, in the case of 

 parts which have become useless, a degeneration of the part, and 

 therefore also of its determinant must inevitably take place ; then we 

 must conclude that processes such as I have assumed are running 

 their course within the germ-plasm, and we can do this with as much 

 certainty as we were able to infer, from the phenomena of adaptation, 

 the selection-value of their initial stages. The fact of the degeneration 

 of disused parts seems to me to aflbrd irrefutable proof that the 

 fluctuations within the germ-plasm are the real root of all lieredltary 

 variation, and the preliminary condition for the occurrence of the 

 Darwin-Wallace factor of selection. Germinal selection supplies the 

 stones out of which personal selection builds her temples and palaces : 

 adaptations. The importance for the theory of the process of degenera- 

 tion of disused parts cannot be over-estimated, especially when it 

 occurs in sterile animal forms, where we are free from the doubt as to 

 the alleged Lamarckian factor which is apt to confuse our ideas 

 in regard to other cases. 



If we regard the variation of the many determinants concerned in 

 the transformation of the female into the sterile worker as having 

 come about through the gradual transformation of the ids into 

 worker-ids, we shall see that the germ-plasm of the sexual ants must 

 contain three kinds of ids, male, female, and worker ids, or if the 

 workers have diverged into soldiers and nest-builders, then four 

 kinds. We understand that the worker-ids arose because their 

 determinants struck out a useful path of variation, whether upward 

 or downward, and that they continued in this path until the highest 

 attainable degree of utility of the parts determined was reached. 

 But in addition to the organs of positive or negative selection-value, 

 there were some which were indifferent as far as the success and 

 especially the functional capacity of the workers was concerned : 

 wings, ovarian tubes, receptaculnm semini% a number of the facets of 

 the eye, perhaps even the whole eye. As to the ovarian tubes it 

 is possible that their degeneration was an advantage for the workers, 

 in saving energy, and if so selection would favour the degeneration ; 

 but how could the presence of eyes diminish the usefulness of the 

 workers to the colony? or the minute receptavnlnm temuiM, or even 



