6 TABOO AND GENETICS 



known as conjugation, and is seen among 

 Paramecia and some other species to-day. Its 

 value is probably a reinvigoration of the vitahty 

 of the individual. Next there was probably a 

 tendency for the organism to break up into 

 many parts which subsequentlj^ united with 

 each other. Gradually some of these uniting 

 cells came to contain more food material than 

 the others. As a result of their increased size, 

 they possessed less power of motion than the 

 others, and in time lost their cilia (or flagella) 

 entirely and were brought into contact with the 

 smaller cells only by the motion of the latter. 

 Finally, in colonial forms, most of the cells in 

 the colony ceased to have any share in repro- 

 duction, that function being relegated to the 

 activities of a few cells which broke away and 

 united with others similarly adrift. These cells 

 functioning for reproduction continued to dif- 

 ferentiate more and more, until large ova 

 and small, motiles permtozoa were definitely 

 developed. 



The clearest evidences as to the stages in the 

 evolution of sexual reproduction is found in the 

 plant world among the green algae. (3.), In 

 the lower orders of one-celled algae, reproduction 

 takes place by simple cell division. In some 

 families, this simple division results in the 

 production of several new individuals instead 

 of only two from each parent cell. A slightly 



