WHAT IS PHYSICAL LIFE 

 the hairs of the eyebrows or those of any 

 other part, a special arrangement of the 

 cells at their roots had to be provided. 

 Then to keep the eyelids from sticking 

 together in sleep, appear rows of twenty 

 to thirty very peculiar glands composed 

 of straight tubes with buds, on their sides, 

 and secreting in their special cells an 

 oily substance different in chemical com- 

 position from any other secretion, etc., 

 etc. 



Such are the visible structures of an 

 eyelid, but, as every medical student 

 knows to his sorrow, the microscope has 

 more than quadrupled the number of facts 

 which he must learn about the structures 

 of organs, all of which have to do with 

 fitness. In the case of the eyelid he may 

 well add facts about the beginning of eye- 

 lids in both human and in comparative 

 embryology. 



But to stop in the consideration of adap- 

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