428 Louise Hoyt Gregory 



or four individuals. This process must be considered an inter- 

 mediate stage between ordinary division and true sporulation. 

 The formation of two individuals only within the cyst has been 

 found to be an indication of low vitality of the protoplasm. 



7 Permanent cysts are formed under certain conditions, such 

 as unusual heat or cold, or lack of food. Experiment shows there 

 is no general rule for the recovery of the normal condition after the 

 organism has formed a permanent cyst. Often the same abrupt 

 changes that caused encystment will bring about the free living 

 condition. 



8 Experiments on regeneration also show that Tillina possesses 

 a high order of regenerative power. In twenty-four hours an 

 anterior or a posterior half of the body will regenerate its lost 

 half, and divide to form two daughter individuals. 



The few centrifuging experiments that were made demonstrate 

 the lability of the protoplasm. In every case the nucleus was shifted 

 forward, and the pigment which ordinarily was present only in 

 the posterior lobe, was scattered throughout the protoplasm, or 

 sent in a mass to the anterior end. 



9 Conjugation was not observed, although all possible means 

 to bring about favorable conditions were employed. 



10 Two cultures of Tillina magna have been carried on. Cul- 

 ture A, consisting of 210 generations, extended from November i, 

 1906, to February 18, 1907; culture B extending from November i, 

 1906, to December 15, 1907, having passed through 548 genera- 

 tions. The life history of each culture is represented by a curve 

 plotted from the averages of the four lines in each culture, and 

 again for ten day periods. 



1 1 The curve which represents the general vitality of the proto- 

 plasm shows the normal rhythmic fluctuations observed by Wood- 

 ruff". 



12 The protoplasm of Tillina is not as sensitive to changes in 

 environment as that of other forms. Treatments with KjHPO^, 

 beef, pancreatin, calf's brain, caused only a slight increase in the 

 division rate. Rejuvenation took place, but only to a slight degree. 

 Since the term rejuvenation must be a relative one only, the term 

 cycle loses its value, and we may consider the life histories of Til- 

 lina, Paramecium and Oxytricha as composed of one cycle. 



