LIFE CYCLE OF NASSULA ORNATA AND N. ELEGANS. 239 



into close contact with the point at which the contractile vacuole 

 is formed. As the minute vacuoles come together they fuse to 

 form a larger vacuole, which, when its maximum size is reached, 

 is discharged. Thus there can always be seen a larger contractile 

 vacuole with smaller vacuoles of various sizes surrounding it, 

 while others are drifting through the cytoplasm toward it. At 

 the point of excretion is situated a wedge-shaped pore connecting 

 the contractile vacuole with the outside of the animal, and 

 through which the waste material passes. Waste material is 

 discharged at the rate of about eighty seconds. 



Nassula thrives only on Oscillatoria. Although I have ob- 

 served Nassula containing a few desmids, I have never been able 

 to maintain a culture using desmids as food. Nassula divides by 

 transverse fission. The nuclear conditions during division have 

 not yet been completely worked out but work is being done at 

 the present time on this subject. Binary fission is found to occur 

 more frequently in older cultures. 



2. No WARRANT FOR Two SPECIES. 



The amount of food present plays a great part in the life 

 history of Nassula. As long as there is an abundance of Oscil- 

 latoria the animals, which were classified as N. ornata by Eheren- 

 berg, live and multiply in the normal way and continue to present 

 the color, size and contour of TV. ornata. But as the food supply 

 becomes exhausted they undergo noticeable changes in these 

 features. As stated above N. ornata is normally ovate or 

 cylindrical, brown or dark green in color and about 200 micra 

 long, but as the food supply diminishes the animal becomes 

 very much smaller and is decidedly longer than it is wide. The 

 color of the food vacuoles changes to a faint red. In this condi- 

 tion it meets all descriptions of N. elegans. If, when this stage 

 is reached, Oscillatoria is fed to the animals, they immediately 

 attach themselves to the filaments to feed. Several hours later 

 they will be seen to contain numerous food vacuoles of very 

 dark color and their normal size is again reached, now meeting 

 Eherenberg's description of N. ornata. Thus, by withholding 

 food, N. ornata may be made to assume the characteristics of N. 

 elegans. Age of the culture also, as over against lack of food, 



