394 Louise Hoyt Gregory 



record shows that this rate of division may rise to 2.5 divisions per 

 day (25 divisions in ten days), and that it may sink as low as .3 

 of a division per day (3 divisions in ten days). (These figures 

 represent the average of the division rates of four individuals for 

 ten day periods.) On comparing the frequency of division with 

 that of Paramecium aurelia, Calkins ('02, '04), and with that of 

 Oxytricha fallax, Woodruff ('05), the records showthat the division 

 rate of Paramecium varies from a maximum of 1.7 divisions per 

 day, to .07 divisions per day (in other words, from seventeen to 

 seven-tenths division in ten days); while that of Oxytricha varies 

 from 3.5 to .2 divisions per day (or from thirty-five to two divi- 

 sions in ten days). These records show that the division rate of 

 Tillina never reaches the height of that of Oxytricha, neither is it 

 able to remain at such a low rate without dying out, as that of 

 either Oxytricha or Paramecium. The protoplasm of Tillina 

 seems to lack the responsive as well as the endurance power of 

 these two other forms. 



When the young individual breaks from the cyst it is about one- 

 fourth the normal size, but perfectly formed, containing few if 

 any food vacuoles. It swims about, taking in food and growing 

 rapidly until in about six hours it has reached its normal size, 

 and is well filled with food vacuoles, which gives it a dark color. 

 As Biitschli states, it seems probable that these cysts are usually 

 formed after the body has reached its maximum size. This can- 

 not be the only condition, as he cites the case of Amphileptus, 

 which encysts in order to digest. I have found cysts varying in 

 size, showing that the capsules may be formed when the maxi- 

 mum size of the individuals has not been reached. 



The first indication of a preparation for division is the notice- 

 able change in movement. This gradually becomes slower and 

 slower until finally, the individual comes to rest on the bottom of 

 the depression slide, or near the glass supports. The cilia tem- 

 porarily disappear. A thin membrane is then secreted covering 

 the entire surface of the body, and rotation begins within the newly 

 formed membrane, indicating the reappearance of the cilia. Ex- 

 cretory particles are discharged from the posterior region. As 

 the rotation proceeds, the normal elongated bean shape is grad- 



