i8o THE BIOLOGY OF THE SEASONS 



in the life-history of a frog or a butterfly. There is, indeed, 

 a very interesting " critical point/ 1 as it is called, when for 

 the first time the specific characteristics emerge. They have 

 always been there, of course, but have not hitherto found 

 more than generalised expression, as far as we can see. But 

 there is no crisis at that " critical point," so far as we know. 

 The process is smooth and orderly ; it is like the unfolding of 

 a bud, except that there are no visible preformed parts ; it is 

 like the working out of an idea in a master-mind who has no 

 hesitation or loose-ends or fluffiness in his concepts. 



It may take a long time, comparatively speaking six 

 weeks in the condor, three in the fowl, two in the finch a 

 long time compared with the extreme rapidity with which the 

 complex architecture of many an insect is built up. And yet 

 what a short time, when we remember the thousands and 

 thousands of cell-divisions that have to occur, each as complex 

 a business as the crowning of a king ! What a short time, 

 when we remember that the developing embryo begins as a 

 single cell, with a nucleus half paternal, half maternal, andthat 

 it becomes within the shell a bird, which may be able to run 

 about whenever the shell is broken, which is in one family 

 (Mound-birds) able to fly when it is born. What a short time, 

 when we remember that the developing bird has to re- 

 capitulate in some measure the racial history of Vertebrates, 

 to climb up its own genealogical tree. 



The stages of development are, in the case of a few birds, 

 such as hen, duck, and even kiwi, so well known from day 

 to day, that exact figures and models are obtainable. There is 

 no doubt whatever that some of the stages are only intelligible 

 when we look backwards as well as forwards. They have a 

 retrospective as well as a prospective significance ; they hint 

 at past history. Thus there are functionless gill-clefts which 

 point back to an extremely remote aquatic ancestry. 



The luminous idea that development resumes evolution, 



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