106 



THE AMEEICAN NATURALIST [Vol. XLIII 



restricted meaning for the theory of descent with modi- 

 fication through variation if it were clear that Darwin 

 always meant fluctuating variation when he used the word 

 variation. 



On page 156 he says : 



Why should not nature take a sudden leap from structure to struc- 

 ture? On the theory of natural selection we can clearly understand 

 why she should not; for natural selection selects only by taking 

 advantage of slight successive variations; she can never take a great 

 and sudden leap, but must advance by short and sure, though slow 

 steps. 



In attempting to explain the puzzling phenomenon of 

 the so-called neuter, really undeveloped female animals, 

 he says : 



As natural selection acts only by the accumulation of slight modi- 

 fication of structure or instinct, each profitable to the individual under 

 its conditions of life, it may reasonably be asked, how a long and 

 gradual succession of modified architectural instincts, all tending 

 towards the present perfect plan of construction, could have profited the 

 progenitors of the hive-bee? 



The answer to this query, by the way, begins with a 

 sentence which has a very modern sound : 



This difficulty, though appearing insuperable, is lessened, or, as I 

 believe, disappears, when it is remembered that selection may be applied 

 to the family, as well as to the individual, and maij thus gain the desired 

 end (pp. 229-230). 



The following utterance should be read with Darwin's 

 main thesis in mind : 



7Q been drawn from the foregoing sen- 

 )arwin had written : If numerous species, 



started into life by variations greater 

 variations, as that term will be under- 

 lining of the twentieth century, the fact 



the theory of evolution through natural 



lis concluding chapter he makes use of 



