The Life History of Tillina Magna 393 



in 1856, descr bed a similar process in Otostoma, and Stein in 

 1859 the same for Colpoda cucullus. Biitschli, in his work of 

 1888, has brought together the results of previous [investigations, 

 and has class fied those forming division cysts into three groups 

 as follows : 



Group I. Those which always form division cysts before sim- 

 ple division takes place: Colpoda cucullus, Holophrya multi- 

 cilia, Amphileptus, Trichorhynchus, Lachrymaria. 



Group 2. Those in which it is doubtful if cysts are always 

 formed before division: Prorodon, Actinobolus, Holophrya gula, 

 Enchylys tarda, Ophryoglena, and here Biitschli places Tillina, 

 wh ch, I believe, rightly belongs in the first group. 



Group 5. Those which may or may not encyst before division: 

 Leucophrys patula. Glaucoma scintillans. 



Today the most complete, and in fact, the only detailed descrip- 

 tion of division cyst formation is that published by Rhumbler in 

 1888, in his paper entitled "A Study of Cyst Formation and the 

 Developmental History of Colpoda cucullus." The division 

 cysts may be either oval bodies in which the protoplasm divides 

 but once, forming two individuals, or spherical bodies in which 

 one or two divisions may take place, resulting in the formation 

 of two or four individuals. He describes a permanent opening 

 in the surrounding membrane of these division cysts through 

 which the contractile vacuole discharges its contents during the 

 early history of the formation of the cyst. Later the contractile 

 vacuole rotates, and its contents are discharged within the mem- 

 brane outside of the body. The newly formed individuals make 

 their escape through the opening in the membrane. 



Reproduction in the case of Tillina takes place exclusively by 

 the formation of spherical cysts in which the protoplasm may 

 divide once or twice, to form two or four individuals. The forma- 

 tion of these cysts varies in frequency depending a great deal upon 

 the amount of food present. Under favorable conditions, when 

 the division energy is normal, and the food has been given at regu- 

 lar intervals, each individual will encyst on the average of once 

 a day, and by two divisions will give rise to four young individuals, 

 the entire process covering a period of about twelve hours. The 



