CONJUGATION 



51 



little tunnel into the other cell. In this cell the two masses 

 fuse as completely as the gametes of Ulothrix did. The 

 new body, made up of the protoplasm and nuclei of the 

 cells, forms a wall about itself inside the w^U of the 

 mother cell. 



In the meantime the other cells of the two filaments 

 have been doing the same thing. Thus a row of bodies 

 may be found in one of the mating filaments, while the 

 other filament will be just a row of empty cells. This is 

 conjugation also. Later each of these united bodies 

 germinates and begins a new filament, which again 

 increases by division. 



5. Paramecium. This extremely active little animal is so 

 abundant and so transparent that it is very satisfactory 

 for students to study with the microscope. It reproduces 

 by fission, much as the bacteria do. But it frequently 

 varies this by another performance no less interesting. 

 Ordinarily paramecia swim about without paying much 



attention to each 



^^^mm^wmimi/m 



other. At certain 

 times, however, ow- 

 ing to causes we 

 know very little 

 about, they begin to 



unite in pairs. They 



Figure 13. Para;«^r?'«;«, one of the protozoa, , , f.^co I'nf/-. r^-na 



magnified. This is a common, one-celled ani- ^^ "OI IliSe mio one, 



mal, abundant in stagnant water. It reproduces ^g other cells we 



rapidly by division of the who'e body into two 



offspring. Occasionally fusion of two individuals have Studied in this 

 occurs. Paramecium moves actively by means , rpi i • 



of the lashing movements of its cilia, indicated in chapter, i hey brmg 

 the drawing by the fringe of lines. their mouths to- 



gether, and for a considerable time swim round side by 

 side as one animal. While they are together thus the 

 nucleus in each divides, and a part of the nucleus of each 

 Paramecium passes into the other by way of the mouth. 

 This incoming nucleus in each case unites with the part 

 of the nucleus of the other which it finds remaining. Each 



