-^4 



LIFE : OUTLINES OF GENERAL BIOLOGY 



simple. What we wish to suggest is the consideration of development 

 not as necessarily Ixnind up with the making of a new organism 

 along the usual sexual re]^roduction lines, but as a process linked 

 back from this tNi^ical embryonic development to the development 

 of bud and fragment, and thence to the replacement of lost parts, 

 to re-differentiation after de-diflerentiation, to the mending of 

 wounds — back and back to the self-preservative repair of wear- 

 and-tear effects — back further still to the self -preservative meta- 

 bolism which we have seen reiison to regard as fundamentally 

 characteristic i)f the organism. Many statements of the characteristic 

 features of an organism have been proposed; we submit that ours 

 Ls so far unified. I'or the jx^rsistence of intactncss leads on to growth, 

 and growth to multiplication, and all three to development. 



From the days of Aristotle, though often with long interruptions, 

 naturalists have lx»en peering into the common miracle of every- 

 day life — tlie development of the chick out of a minute clear drop 



iMC. 7. 



A.Ivrntitiotis HikIs \^\ ) lorniinf? at the Sides of a Leaf (L) of Bryophyllum 



calycinum. 



of living matter, lying on the top of the yolk of the egg; and though 

 many details of the process are known and some of the factors at 

 work, w«> still stand amazed at the condensation of individuality 

 intf) a germ-cell and its re-exjiression lus a young creature. In his 

 40th ICxerritation on "the efluient cause of the chicken", Harvey 

 ipiaintly .xpresM-d, early in the seventeenth century, his sense of 

 the baffling nature of the problem: "Although it be a known thing 

 subscriU'd by all, that the f net us assumes its original and birth 

 frrim the male and female, and consequently that the egge is pro- 

 ducrfl by the cock and henne, and the chicken out of the egge, yet 

 neither the srhrK)ls of ])hysicians nor Aristotle's discerning brain 

 have disclosed the manner how the cock and its seed doth mint 

 and coine the chicken out of the egge." 



In his discussions of the characteristics of living creatures, 

 Huxley was wont to lay emphasis on what he called "cyclical 

 rlevelopment". Within the embryo-sac, within the ovule, within 



