WHAT IS PHYSICAL LIFE 



layer develop in time, by various inf old- 

 ings, the nervous and some skin tissues; 

 from the second the connective tissue, the 

 muscles, blood-vessels, and bones; and 

 from the third the lining of the alimentary 

 canal and its associated viscera, etc. If the 

 further steps of development of organs 

 out of these primary divisions had not 

 been carefully followed, no one would 

 dream what the word " differentiation " 

 used by biologists to denote the process, 

 means. It means that each cell, as growth 

 goes on, takes its place where it ought to, 

 in other words along predetermined lines. 

 Every one of the many and diverse tissues, 

 for example, which make up an eye, fit 

 their places as parts of an eye and not of 

 an ear. And so of the component parts of 

 all the other organs. Fitness local, fitness 

 general, fitness universal meets us at every 

 turn, and so sure is this interdependence 

 and interrelation of parts that an anato- 

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