480 



On Bacterium termo and Micrococcus. [June 20, 



wall gives way, and the segments as they separate slowly draw out 

 a thin viscous thread of protoplasm. One segment generally fixes 

 itself to the cover glass, while the other wriggles about in all direc- 

 tions, moving and resting by turns, until the almost invisible thread 

 gives way in the middle so as to form two cilia. Thus the first 

 formed motile rods should only have one cilium, and such are occa- 

 sionally seen, but are probably soon supplanted by their more active 

 biciliate progeny. After being alternately at rest and in motion for 

 an indefinite period, they may rise to the surface of the fluid to form a 

 zooglcea (j) and after some time again become motile. 



In Series II the spore immediately after germinating develops into 

 a long t filament or unbranched hypha, which interweaves with others 

 to form a mycelium. The protoplasm of the filaments soon contracts 

 into rows of " chlamy do spores " (/) which either escape through the 

 cellulose walls, or are set free by the disintegration of the hypha (i j k). 

 When once free they may either form a zooglcea (m) or germinate 

 immediately. 



In Series III the spore divides into four sporules (e), which, while 

 separating, move very energetically. This takes place when the nu- 

 tritive fluid is becoming exhausted, the sporules not germinating until 

 more nourishment is obtainable. If fresh pabulum be not added 

 the sporules may continue dividing (Series IV) so as to form large 

 finely granular spheres (efg), compound masses resulting from the 

 division of several adjacent spores. These disintegrate, setting free 

 numerous small round particles (Ji) which in suitable media enlarge 

 and germinate (j). 



Leaving Bacillus, Series V shows the life-cycle of Bacterium termo. 

 The round spore germinates into a short rod (5), which either 

 divides into a chain (<s), or into separate rods, with resting and motile 

 stages alternating (/ g), while the short rods may lengthen into 

 delicate spore-bearing filaments (Ji i). The thorough correspondence 

 of all this with Series I and II of Bacillus is very obvious and 

 suggestive. Moreover, these spores (j) exactly resemble the Micro- 

 coccus represented below in Series VI. 



Here the spore-like Micrococcus becomes dumbbell-shaped and 

 divides into two (c), which again divide, and so on indefinitely, a pre- 

 paration of Micrococci kept for three months having shown no tendency 

 to germinate into rods. Resting and motile stages (g), chains (/), and 

 zooglcea (ji) are often observed. 



EXPLANATION" OF THE PLATE. 



Series I — IV. Phases in Life-History of Bacillus. 



„ V. „ „ Bacterium termo. 



„ YI. „ Micrococcus. 



