i 9 2 THE POPULAR SCIENCE MONTHLY, 



ures from I to XII is one third of the distance from the outer circle 

 toward the center. If the face of the clock is white, the figures and 

 the hands should be black. If the face is black, or any dark color, the 

 figures and hands should be either white or gilt. The dials of tower- 

 clocks are frequently illuminated by gas or electricity, so that the time 

 may be easily determined at night. 



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THE FACTOKS OF OEGAKLC EYOLUTIOK 



By HEEBEET SPENCEE. 



in. 



LIMITED, as thus far drawn, to a certain common trait of those 

 minute organisms which are mostly below the reach of unaided 

 vision, the foregoing conclusion appears trivial enough. But it ceases 

 to appear trivial on passing beyond these limits, and observing the im- 

 plications, direct and indirect, as they concern plants and animals of 

 sensible sizes. 



Popular expositions of science have so far familiarized many read- 

 ers with a certain fundamental trait of living things around, that they 

 have ceased to perceive how marvellous a trait it is, and until inter- 

 preted by the Theory of Evolution, how utterly mysterious. In past 

 times, the conception of an ordinary plant or animal which prevailed, 

 not throughout the world at large only but among the most instructed, 

 was that it is a single continuous entity. One of these living things 

 was unhesitatingly regarded as being in all respects a unit. Parts it 

 might have, various in their sizes, forms, and compositions ; but these 

 were components of a whole which had been from the beginning in its 

 original nature a whole. Even to naturalists fifty years ago, the as- 

 sertion that a cabbage or a cow, though in one sense a whole, is in 

 another sense a vast society of minute individuals, severally living in 

 greater or less degrees, and some of them maintaining their independ- 

 ent lives unrestrained, would have seemed an absurdity. But this 

 truth which, like so many of the truths established by science, is con- 

 trary to that common sense in which most people have so much confi- 

 dence, has been gradually growing clear since the days when Leeu- 

 wenhoeck and his contemporaries began to examine through lenses the 

 minute structures of common plants and animals. Each improvement 

 in the microscope, while it has widened our knowledge of those minute 

 forms of life described above, has revealed further evidence of the fact 

 that all the larger forms of life consist of units severally allied in their 

 fundamental traits to these minute forms of life. Though, as formu- 

 lated by Schwann and Schleiden, the cell-doctrine has undergone quali- 

 fications of statement ; yet the qualifications have not been such as to 

 militate against the general proposition that organisms visible to the 



