MICROSPIRA COMMA. 475 



when swimming up stream i. e., they all point in nearly 

 the same direction, and lie in irregularly parallel, linear 



FIG. 74. 



Mierospira comma. Impression cover-slip from a colony thirty-four 

 hours' old. 



groups that are formed by one comma being behind 

 the other without being attached to it. 



FIG. 75. 



'' *r ' 7*> 

 < <- **</ 1 ^ 



Involution-forms of microspira comma, as seen in old cultures. 



On cover-slip preparations made from cultures in the 

 ordinary way there is nothing characteristic about the 

 grouping ; but in impression cover-slips made from 

 young cultures the short commas will nearly always be 

 seen in small groups of three or four, lying together in 

 such a way as to have their long axes nearly parallel to 

 one another. (See Fig. 74.) 



In old cultures in which development has ceased it 

 undergoes degenerative changes, and the characteristic 



