CHAPTER VIII. 

 REPRODUCTION. 



The most simple living organisms multiply by division 

 with or without karyo kinetic changes of the nucleus. 

 In most cases such division is binary; that is, results in 

 two of the same general kind; but in special cases, 

 sporulation, it is multiple and gives rise to a varying 

 number of offspring that differ from the parent in being 

 much smaller and also in certain cases in being obliged 

 to pass through a succession of changes before reaching 

 maturity and parental resemblance. Other lowly organ- 

 isms reproduce by a different method known as gemma- 

 tion or budding. In these forms, of which the yeasts 

 will serve as examples, the adult cell throws out a minute 

 bud or excrescence which grows larger and larger and 

 more and more like the parent. As the bud grows, 

 the nucleus of the cell divides by some modification of 

 the karyokinetic process, one-half being retained in 

 the parent cell, the other half passing into the bud which 

 eventually separates as a new individual. 



Inasmuch as both division and gemmation result in 

 the multiplication of a single cell, these methods are 

 described as asexual or monogenetic reproduction. 



The ability of any cell to multiply depends upon its 

 inherited impulses and upon its conditions of life. 

 Thus, though multiplication is continually in progress 

 among the unicellular forms of life, and characterizes 

 the great body of cells among the metaphyta or higher 

 plants, it is found among the metazoa or higher animals 

 only during the period of growth. When maturity 

 i.e., the full size and complete differentiation has been 



181 



