EXPLANATION OF PLATES. 



The figures in plates I, II, and III are camera drawings, made witli the com- 

 binations of Zeiss and Leitz objectives noted and reduced about one third in repro- 

 duction. In Plate IV, Figures 52-55 are reproductions of I'etri dish cultures, and 

 were slightly reduced in the process of photographing; Figures 56-58 are repro- 

 ductions of stender dish cultures, and were slightly magnified. The signs (+) and 

 (— ) are used to denote the opposite strains whenever these are distinguished. 



