THE FOUNDATIONS OF GENETICS 



273 



of nuclear reorganization accompanied by an exchange of nuclear 

 material l)etween individuals. Such a process is akin to sexual 

 reproduction of higher forms and suggests the importance of the 

 nucleus in the vital processes of the cell. It also indicates the 

 possibility of combination of parts of two organisms in a single 

 individual even in the lowest groups. 



Reproduction of Multicellular Organisms. Above the single- 

 celled organisms a process of budding or fission occurs which can 



micronucteus 



gullet 



micronucleus 

 gullet: 



Contractile vacuole 



macronucleuS 



Contractile vacuole 



contractile vacuole 



macronucleuS 



contractile vacuole 



Fig. 157. — Paramecium aurelia dividing by binary fission. 



after Lang.) 



(From Newman, 



also be expected to produce as nearly as possible identical indi- 

 viduals. Hydra, a common fresh-water coelenterate, frequently 

 reproduces in this way (Fig. 158). Among the more highly organ- 

 ized forms, however, sexual reproduction is l^y far the most common 

 process, although sporulation still persists in such highly developed 

 plants as the ferns and parthenogenesis is not rare among animals. 

 All of these cases differ from the more primitive asexual processes 



