BACTERIA. . 41 



trotting horse and considerably less than that of a speeding automobile 

 or a railroad train. 



. REPRODUCTION. 



Reproduction among the bacteria is largely asexual and takes place 

 ordinarily by what is known as binary fission. In addition to this a num- 



QCDODOO 



FIG. 20. The division of bacterial cells (diagrammatic). (After Novy.) 



ber of bacteria go into a resting stage, or produce spores. The spore 

 formation is not, however, a method of multiplication, because usually 

 only a single spore is formed in a cell, but serves to tide the organism 

 through unfavorable conditions. 



FlG. 21. i-n, Bacterium gammari, resting nuclei, and in various stages of mitosis. 

 12-16, a filamentous bacterium in the digestive tract of Bryodrilus. 13-14 and 15, ex- 

 tremities of the filaments with nuclei. 16, old filaments, two cells are without nuclei. 

 (After Vejdovsky from Guilliermond review, Bull. Inst. Past.} 



VEGETATIVE MULTIPLICATION. This is accomplished by means of 

 binary fission (Fig. 20). When a bacterium has reached maturity, fis- 

 sion begins. This change in the cell is not customarily regarded as 

 preceded by any series of changes comparable to karyokinesis (mitosis) 



