METAMORPHOSIS. 209 



ular combination of forces acting at the proper 

 moment. These combinations of forces follow each 

 other in fixed and regular sequence, and blend 

 £)ne with the other. As the sequence is generally 

 the same for all organisms of a species, so the 

 organisms resemble each other. Where the se- 

 quence for any individual differs from the sequence 

 for the rest of the species, that individual will 

 differ in growth from the rest of the species, pro- 

 vided always that the difference be not so great 

 as to destroy the life of the individual. 



The changes of these combinations of forces 

 are not equal in extent or activity at all points of 

 the sequence. Thus in the earliest development 

 of an organism, the changes of development are 

 more marked and more rapid — the earliest stages of 

 development having been repeated most often. In 

 the latter stages, as the organism approaches 

 maturity, the changes become slower, less marked 

 in degree, and less certain — the very last stages 

 that appear in some cases being wholly omitted 

 in others. Apparently, these very last reactions 

 of the organic matter to the forces at work upon it 

 have not been repeated often enough to become 

 firmly associated with the older and stronger part 

 of the hereditary impulse. The power of the hered- 

 itary impulse, in the latter stages, loses strength 



