EFFECTS OF THYROID ON PARAMAECIUM 559 



some of which had become considerably enlarged, while others 

 had disappeared. One canal of each system finally rounded up 

 and began pulsating (apparently emptying its contents to the 

 exterior). Some of the reduced feeding canals were acquired, 

 others formed de novo and in a short time all the appearance of a 

 miniature contractile vacuole with a complete feeding system 

 were assumed. A few spasmodic contractions were recorded, 

 during which time the vacuole increased in size, before the form 

 was accidentally destroyed through the evaporation of the drop 

 of water in which I was observing it. I have not yet had the 

 opportunity of repeating this observation, but I am convinced 



Fig. 11 Paiamaecium caudatum after 160 days thyroid treatment, showing 

 non-contractile excretory vacuoles. Drawn from life. 



Fig. 12 Same individual shown in figure 11 after expulsion of non-contrac- 

 tile vacuole. Drawn from life. 



that this is the mode of formation of the giant non-contractile 

 vacuoles characteristic of my thyroid fed lines. 



The fate of these large vacuoles is also of interest. I have re- 

 peatedly observed them burst, pouring out their contents to 

 the exterior. No apparent effect was produced upon the Para- 

 maecium except a shrinking of the protoplasm where the large 

 vacuole had been located, resulting in the formation of a tailed 

 or hooked Paramaecium similar to those upon which not a few 

 studies of heredity have been made. The physiological functions 

 of the Paramaecium do not appear to be in the last injured, al- 

 though the size of the individual be reduced a half by such an 

 explosion. Figure 12 represents the same individual as figure 



