CORRELATION OF GROWTH. 175 



and therefore cannot be regarded as in a process of 

 gradual disappearance owing to the loss of function 

 and stimuli of growth. 



We find the same singleness of plan influencing 

 growth where the growing parts are not completely 

 separated but remain dependent upon one another. 

 Thus the different segments of a worm, which grow 

 by budding from one another, are similar both in 

 external appearance and in internal organs. In as- 

 cending the scale of segmented animals, we find 

 more and more that the different influences of a 

 more complex existence have modified the particular 

 growth of the various segments, preserving only a 

 general fundamental similarity of structure. How- 

 ever, the change in the development of one segment 

 of an animal seems to influence a change in the 

 development of the other segments — as though the 

 living matter would not learn an entirely new plan 

 for only one segment, but applied it as far as possi- 

 ble to all. Thus Professor Weismann mentions cer- 

 tain eye-like markings which appeared first on one of 

 the anterior segments of a caterpillar, and then 

 developed on the other succeeding segments.^ Pro- 

 fessor Weismann explained satisfactorily the first 

 appearance of the marking on one segment as an 

 instance of protective colouring, whereby the eye- 



1 Weismann, Studies in the Theory of Descent (Macmillan & Co.). 



