I/O 



ARTHUR WHIEE GREELEV. 



FIG. 5. Young Monads devel- 

 oped from the spores within the old 

 cell wall of the resting cell. 



swims away, leaving the empty spore behind. In some cases 

 the spores are not discharged from the resting cell as soon 

 as they are formed, but develope within its walls, so that it 

 is possible to find spores in all stages of development, even the 



young Monads, within the old rest- 

 ing cell. The development of the 

 spores usually occupies from two 

 to four days, although in some cases 

 it may be delayed for a mcuh. longer 

 time. The Monads formed from the 

 spores are at first spherical, and swim 

 about with the characteristic revolv- 

 ing movement of this species of Mo- 

 nas. The cells rapidly become elon- 

 gated, however, and within a short 

 time are indistinguishable in all re- 

 spects from the adult organism. 

 A few typical experiments will be briefly described, as fol- 

 lows :-^ 



Experiment I. On April i i a culture of Monas was placed 

 in the refrigerator at a temperature of i to 4C. The next day 

 examination showed that all the Monads had formed spherical 

 resting cells. Some of these were removed to the temperature 

 of the room, and they immediately developed into the motile 

 form. On April 24 many of the resting cells had broken up 

 into spores. A small number of these resting cells and spores 

 were isolated under the microscope. The resting cells imme- 

 diately developed into the motile Monads as before. On April 

 26 a few of the spores had formed small Monads, but the de- 

 velopment did not go very far because of a lack of oxygen in the 

 closed cells which contained the spores. 



Experiment II. On April 18 a culture of Monas was put 

 on ice at a temperature of i C. On May 3 the culture was 

 removed to a temperature of 6 C. A large number of spores 

 had been formed, a large proportion of them remaining within 

 the resting, cells. On May 6 many of the spores had devel- 

 oped into young Monads. A large number of the Monads were 

 found swimming about within the walls of the resting cells. 



