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WALDO SHUMWAY 



Wallengren, '01), which may appear in paramaecia well pro- 

 vided with food and still forming gastric vacuoles. Food in the 

 case of starved Paramaecia, stimulation in the case of those 

 undergoing a depression period, results in the disappearance of 

 these vacuoles. 



Vacuoles of this description were characteristic of the thyroid 

 Paramaecia of these experiments, especially at times of rapid 

 division. Sample individuals are shown in figures 9, 10 and 11. 

 Examination of the media at such times showed thyroid and 



Fig. 9 Paramaecium caudatum after 220 days thyroid treatment, showing 

 non-contractile excretory vacuoles. Drawn from life. 



Fig. 10 Paramaecium caudatum after 220 days thyroid treatment, showing 

 non-contractile excretory vacuoles. Drawn from life. 



bacterial food present in abundance. Gastric vacuoles were being 

 formed at the normal rate. 



A chance observation may serve to throw some light on the 

 origin of these enormous non-contractile vacuoles. In a Para- 

 maecium under observation it was noticed that the contractile 

 vacuoles had lost their connection with the exterior, although nor- 

 mal in all other respects, swimming about and forming gastric 

 vacuoles. For a considerable time the feeding canals continued 

 normal pulsations, at each of which the vacuole proper became 

 enlarged. Finally the two enlarged vacuoles swung into the 

 center of the cell, presenting all the appearance of the large non- 

 contractile vacuoles characteristic of starved or thyroid fed Para- 

 maecia. My attention was now diverted to the feeding canals, 



