Arthur White Greeley 



the dishes in a refrigerator in which constant temperatures, ranging from 1° to 10° C, 

 could be maintained. For each low-temperature experiment a control experiment 

 was performed at the temperature of the room, and great care was taken that all the 

 conditions, with the exception of temperature, should be identical in the two cases. 



Monas is more sensitive to changes in the temperature than any of the other 

 Protozoa experimented with. Within a few hours after the temperature has been 

 lowered to 4° C. all the Monads in a dish settle to the bottom and 

 cease their progressive movement. At the same time the cell gradu- 

 ally becomes spherical, the flagellum and mouth-opening disappear, 

 and there is formed a resting cell like those already described in the 

 experiments upon Stentor. These resting cells can be kept at a 

 temperature of 4° to 6° C. indefinitely, and will withstand partial 

 FIG. 2 desiccation without losing their power to revert to the normal Monas 



A resting cell of Monas, form wheu they are removed to the temperature of the room. This 



formed by an exposure . ± .-i am £ j. i i -ii • i. j. £ t 



to a temperature of i' reversion to the motile form takes place withm twenty-tour hours 

 c. during six hours. after the room temperature has been reached. The flagellum first 

 makes its appearance and the cells become motile while still in the spherical condi- 

 tion. They soon, however, assume the normal elongated form of the adult Monas. 



If these resting cells of Monas which have been formed at a temperature of 4° to 

 6° C, instead of being returned to the temperature of the room, be placed on ice at a 

 temperature of 1° C, further structural changes take place as a result of this extreme 

 lowering of the temperature. After remaining at a temperature of 1° C for five to 

 seven days, the protoplasmic contents of the resting cells break up into small spherical 

 spores, from two or three to twenty-five in each cell. In most cases these spores are 

 discharged from the resting cells as soon as they are formed. They have thick cell 

 walls, and are non-motile. They may be kept indefinitely at any temperature below 

 8° C, and withstand desiccation perfectly. 



When the spores are removed to the temperature of the room and isolated in 

 small, closed cells under the microscope, their development into the 

 motile Monad can be easily followed. The first attempts to demon- 

 strate the development of the spores failed in several instances 

 because of a lack of oxygen in the closed cells in which the spores 

 were isolated, due to the presence of motile Monads which origi- 

 nated from resting cells isolated with the spores. But finally, at 

 Dr. Loeb's suggestion, some fresh -water Algae were mixed with the 

 spores as soon as they were returned to the temperature of the room. 

 In this way a supply of oxygen was maintained, and the develop- 

 ment of the spores began at once. The first change that can be 

 observed is the appearance of a thin layer of protoplasm which 

 grows out of the spore. This protoplasmic layer develops into a small, spherical cell, 

 which gradually becomes separated from the spores. The cell is at first hardly visible, 



75 



FIG. 3 

 The formation of spores 

 within the resting cell 

 after an exposure to a 

 temperature of 1° C. for 

 five days. 



