130 GENERAL BIOLOGY 



advantage to the species of the phenomenon of 

 reproduction, the replacement of individuals by 

 others from the same stock. Each individual passes 

 through a cycle of birth, youth, maturity, senility, 

 and dissolution, but before the final stages are 

 reached, it normally produces other individuals to 

 take its place. 



Biogenesis. This phenomenon clearly implies a 

 continual stream of life, in which individual succeeds 

 individual like waves on the ocean. The physical 

 connection of the individual with its ancestry is thus 

 obvious. An aphorism of a century ago expresses 

 it, " Omne vivum ex vivo," " all life from [pre- 

 existing] life." But a contrary view was also held 

 until very recent times, viz. that living organisms 

 may arise from non-living matter. This conception, 

 which has been called spontaneous generation or 

 abiogenesis, arose from incomplete or misinterpreted 

 observation. Thus it is a matter of everyday ob- 

 servation that maggots develop in rotting meat. 

 Whence do they come, if not from the meat itself? 

 A generation less well trained in the methods of 

 exact research found no difficulty in accepting just 

 such an hypothesis, but an ingenious Italian, Redi, 

 showed that if the meat be covered with gauze so as 

 to keep out the blow-flies, no maggots ever develop, 

 since these are produced, not from the meat, but 

 only from the eggs which the fly lays on the meat. 

 In brief, it has been conclusively shown, in every 

 instance, that no living forms are to be found to-day, 



