REPRODUCTION IN PARAMECIUM 



267 



Each of the cells which fuse during conjugation is 

 known as a gamete. When very nearly alike they are 

 called isogametes. Conjugation is the result of the 

 fusion of part or all of the cell contents of isogametes. 

 The result of the union is a zygospore. 



mote their germination. Then each zygospore absorbs water, 

 breaks the zygospore case, and forms a new filament as a result 

 of binary fission. There like or isogametes 

 is enough stored food in 

 the zygospore to start the 

 germination and sustain 

 life until the filament can 

 make its own food. 



Sexual reproduction in 

 Paramecium. Paramecia 

 ordinarily reproduce asex- 



ually by binary fission. Occasionally, sexual reproduction takes 

 place. Two cells lie next to and in contact with each other. 

 At the point of contact the cell membranes dissolve. Various 

 complicated changes take place in the nuclei of the two animals. 

 The macronucleus in each breaks up and disintegrates. The 

 micronuclei go through a number of divisions and finally one 

 fragment of each micronucleus passes over and unites with a 

 fragment of the micronucleus in the opposite cell. After this 

 mutual exchange and fusion of micronuclear material, the two 



Paramecia separate, and the micronucleus 

 of each goes through further complicated 

 divisions, which result in the formation of 

 both a micronucleus and a macronucleus. 

 The conjugation of the Paramecia seems 

 to bring about a renewed vigor. In cer- 

 tain species conjugation may occur once in 

 every two or three hundred generations, 

 although these same species may live a very 

 long time, providing conditions are favor- 

 able, without ever reproducing sexually. 



Certain recent experiments have shown that the environment 

 affects the vitality of the Paramecium. By removing wastes and 



A photomicrograph showing 

 the conjugation of Paramecia. 



