UNICELLULAR ORGANISMS 



81 



FIG. 35. BACTERIA WITH FLAGELLA 



A, flagella are distributed over the whole 

 body, a condition called peritrichic; B, flagella 

 grouped together in cluster at one end, called 

 lophotrichic; C, a single flagellum, monolrichic.* 



bacteria (see Fig. 35) have minute flagella, which by lashing to 

 and fro cause them to move. Beyond the points shown in the 

 figures, there is very little to 

 be said concerning the struc- 

 ture of bacteria. 



Reproduction. Bacteria 

 all multiply, by fission, each 

 dividing into twp parts, 

 which again divide when 

 they have grown to the 

 size of the parent cell. 



Spore Formation. Some 

 species of bacteria produce 

 spores in the following man- 

 ner: After growing for a 

 time by division the contents of a single bacterium collect into 

 a rounded mass which becomes surrounded by a hard resisting 

 wall; see Fig. 33 E. This is set free by the breaking of the bac- 

 terium that holds it and is then capable of starting a new series 

 of generations. This clearly resembles the ascospore formation 

 in yeast, except that there is no actual multiplication of indi- 

 viduals, one bacterium giving rise to one spore only. The 

 spores have resisting walls and are able to stand drying and 

 a fairly high degree of heat. Their function is thus that of 

 protecting the race from destruction by drying and heat rather 

 than that of multiplication, the latter function being performed 

 by the process of simple division. 



Bacteria are very widely distributed in nature. They are 

 found in the air, in the soil, in all bodies of water, and, in fact, 

 practically everywhere. They play an extremely important 

 part in the life processes of nature through their relation to all 

 forms of putrefaction, decomposition, and decay. The bacteria 

 are important agents in maintaining the continued fertility 

 of the soil, making it capable of producing crops year after 

 year. A few species live as parasites within human bodies 



*Gr. peri = around 

 Gr. lophos = tuft 

 Gr. monos = one 



+ trix = hair. 



