ELEMENTS OF MICROBIAL CYTOLOGY 25 



toward the posterior end. In the lateral region of the cell it unites 

 with a contractile membrane, the undulating membrane, running in 

 spiral form along the length of the body, of which it is the free end. 

 Flagella are made up of one or more elastic fibers, surrounded by a 

 thin cytoplasmic sheath. 



The vibrating cilia are also contractile appendages, differing from 

 the flagella only in their smaller size. They cover the whole body 

 of the cell, as in the case of infusoria, enabling them to move about 

 very easily in liquids. 



Certain facts lead us to believe that flagella are only transformed 

 pseudopods in which the cytoplasmic structure has changed and at the 

 same time the kind of movement. Thread- 

 like pseudopods are found with a rapid 

 rhythmic movement which may serve as 

 intermediate forms. Be that as it may, the 

 method of forming these organs is of special 

 interest. Apparently they are formed under 

 the influence and at the expense of the cen- Fig. 14. — Organs of loco- 

 triole motion in bacteria. A, B. 



^ ' , „, „ , r, 1, .1 subtiHs. {After ,Fischer) 



In the Flagellata the nagellum is always b, Microspira comma. 



inserted in the centriole or in a similar organ W(f»;.i^wc*«»' o«^ Migula.) 



, . , . , , ., C, Spinllvm, rubrum. 



which appears to issue from the centriole. 



It is not rare to find in cellular division some cells in which the nucleus 



is dividing with a centriole at each of its poles. Each serves as a point 



of insertion for a flagellum (Fig. 15, A, D,E). 



According to recent works, the flagellum is formed in general 

 in one of two somewhat different methods. 



In the first case, the centriole divides itself by an elongation, followed 

 by a contraction into two centrioles which remain united to each 

 other by means of a fine thread, the cenfrodesmose. The centrodesmose 

 then elongates, dragged by the centrioles, as far as possible from the 

 nucleus, and transforms itself into a flagellum. 



In the second case, the centriole divides itself a first time just as 

 in the preceding case, but the centriole farthest from the nucleus im- 

 mediately undergoes a second division, thus making three centrioles. 

 The one nearest the nucleus remains a centriole during nuclear division. 

 The centriole situated somewhat farther from the nucleus becomes the 

 point of insertion for the flagellum, and is called the Uepharoplast or hasal 



