304 GEORGE W. TANNREUTHER. 



the evaporation. Few free swimming forms were found when 

 collected. But within twenty four hours great numbers would 

 escape from the cysts. Conjugation occurred immediately at the 

 beginning of the free swimming stage. The period of conjugation 

 lasts from three to four or more hours. The ex-con jugants 

 remained in the active swimming stage indefinitely, dependent 

 upon external conditions. 



Encystment is quite common, it may occur at any period in 

 their life history and serves more for protection in carrying them 

 over adverse conditions, due to extreme temperature or drought. 

 The cysts in many cases are large, spacious and permit freedom of 

 motion within (Fig. 2a). In the formation of the cysts the 

 animal always contracts, assumes a spherical shape and rotates 

 rapidly while secreting the cyst. The secretion is evenly dis- 

 tributed by the aid of the beating cilia. The animal usually 

 forms its cyst in contact with some fine sediment, which acts more 

 as a background. The cysts show considerable variation as to 

 their flexibility and thickness (Fig. 2a-/). The cysts are either 

 thin or temporary and thick or permanent. The animal may 

 remain within the temporary cyst but a short time, then escape, 

 and immediately begin the formation of a new cyst. Large 

 numbers of cysts are often found in immediate contact and form a 

 sort of network, as in Fig. 2. The animal just before escaping 

 from the cyst becomes unusually active presses against one side of 

 the cyst wall and breaks through. The permanent cysts differ 

 from the temporary cysts, in that they are thicker, due to the 

 secretion of new concentric layers within the first, until there is 

 little space left for the animal within (Fig. 2/). After the perma- 

 nent cyst is completed the animal becomes quiescent and remains 

 in this condition indefinitely, at least until internal reorganization 

 is complete. 



In studying the formation of the cysts under the cover slip, it 

 was found that the temporary cysts were often formed within 

 thirty minutes, while the thick or permanent cysts required from 

 three to five hours for their complete formation. In some of the 

 permanent cyst under observation the animal remained quiescent 

 for three days or more and then began a very rapid rotary motion 

 within and soon escaped. The animal evidently must secrete 



