DIV. I 



THALLOPHYTA 



371 



undergo a mucilaginous swelling, the cells or cell-rows being embedded 

 in the gelatinous mass. This stage of development is termed ZOOGLOEA. 



In contradistinction to these unicellular HAPLOBACTERIA the 

 TRICHOBACTERIA form filaments which as a rule are simple (Leptothrix, 

 Beggiatoa, Crenothrix). In Cladothrir, however, they exhibit what is 

 termed false branching. This comes about by the distal portion of 

 the filament being left on one side while the original line is continued 

 by the division of the cell behind the break. 



Many Bacteria are motile. Their independent movements are 

 due to the vibration and contraction of fine protoplasmic cilia (*) m 

 These cilia, according to A. FISCHER, are either distributed over 

 the whole surface of the cells (peritrichous) (e.g. Bacillus subtilis, Fig. 

 295 a, d Bacillus typhi, Fig. 293 c; Bacillus tetani, Fig. 298 e), or 



FIG. 2i'3. Types of arrangement of flagella. a, 

 Vibrio cholerae ; b, d, Spirillum undula ; d, 

 development of a new bunch of cilia in divi- 

 sion ; c, Bacillus typhi ; e, Bacillus subtilis. 

 (x 22oO. After A. FISCHER.) 



FIG. 294. Cladothrix dichotoma. Formation 

 of swarm-cells from the .cells of the fila- 

 ment, (x 1000. After A. FISCHER.) 



they spring from a single point either as a single flagellum (mono- 

 trichous) or as a group (lophotrichous). A single, polar flagellum 

 occurs in Vibrio cholerae (Fig. 293 a) ; a polar terminal tuft of 

 flagella in Spirillum undula (Fig. 293 b, d) ; a lateral tuft in the 

 swarm-spores of Cladothrix (Fig. 294). The ciliary tufts may become 

 so closely intertwined as to present the appearance of a single thick 

 flagellum. The cilia are never drawn within the body of the 

 cell, but undergo dissolution before the formation of spores takes 

 place, or under unfavourable conditions (Fig. 293 e). 



Multiplication of the individual is accomplished vegetatively by 

 the active division or fission of the cells ; the preservation and dis- 

 tribution of the species by the asexual formation of resting spores. 

 These arise as endospores (Figs. 295 c, 296 e, j) in the middle or 

 at one end of a cell by the inner portion of the protoplasm separat- 

 ing itself from the peripheral, and surrounding itself with a thick 

 membrane. The membrane of the mother cell becomes swollen and 



