342 ANIMAL LIFE 



25. ORIGIN OF THE DIVERSE FORMS OF ANIMAL LIFE 



A study of the universe and of the rocks forming the 

 crust of the earth shows that conditions were such many 

 millions of years ago that no life could have existed on this 

 planet. It is therefore evident that living things at some 

 time in the past must either have been developed from life- 

 less material or reached the earth from some other heavenly 

 body. Scientists find no evidence in favor of the latter 

 theory, and we are therefore forced to believe that at some 

 period after the surface of the earth became cool, spon- 

 taneous generation occurred, i.e., a particle of lifeless earth 

 was transformed into a living thing. 



The conception of the ancient as well as some of the 

 more modern philosophers in regard to the origin of animals 

 is entirely erroneous. Aristotle held that some animals 

 spring from putrid matter, that certain insects develop 

 from dew, that worms originate in the mud of wells, that 

 fleas arise from very small portions of corrupted matter, 

 and bugs proceed from the moisture on animal bodies, and 

 lice from the flesh of other creatures. Van Helmont, of 

 the seventeenth century, gives detailed directions for 

 creating mice out of wheat and stagnant water. The 

 learned Alexander Ross, about the year 1700, declares 

 there is no doubt that worms are generated from cheese 

 and that butterflies, locusts, grasshoppers, snails, eels, and 

 such like originate from putrid matter. 



Before the days of the compound microscope and care- 

 ful scientific research, spontaneous generation was thought 

 to be going on continually, but by numerous carefully con- 

 ducted experiments of Spallanzani, Schultze, Schwann, 



