The Life History of Tillina Magna 427 



nucleus were abnormal and germinal death followed. In neither 

 case of depression was the size of the nucleus abnormal in its rela- 

 tion to the size of the cell body. Because of these facts, and of 

 those resulting from actual measurements of Tillina, it seems 

 more probable that if the nucleus is greatly enlarged as in the case 

 of Stylonychia, this must be explained as the result, rather than 

 the cause of the depression, and the definite increase in proto- 

 plasmic material which Minot found, is the result of senescence 

 not the cause. In other words, the evidence at the present time 

 seems to indicate that the morphological changes taking place in 

 the cell are due to physiological changes in the metabolic action 

 of the cell. 



IX SUMMARY 



1 Tillina magna is a ciliated infusorian, belonging to the 

 family Chiliferidae, suborder Trichostomina, order Heterotrichida. 

 Wild material was found but once only in an infusion of horse 

 manure. All attempts to find more material were unsuccessful 

 and the possibility arises that the organism is an intestinal para- 

 site of the horse. 



2 The size varies from ioo-200/« in length, and from yc-iSo/z 

 in breadth. 



3 The organism is recognized easily by the presence of the 

 characteristic dorsal posterior lobe, a portion of which extends 

 as a tongue into the peristomial region, finally disappearing in 

 the floor of the oesophagus. The entire structure is covered with 

 long fine cilia. 



4 The surface of the body is covered with striations which 

 indicate the insertion of the cilia. The cilia have their origin in 

 the basal bodies which lie in the cortical plasm at the corners of 

 the raised fields into which the surface of the body is divided. 



5 The nuclear structure consists of a large macro-nucleus and 

 a varying number of very small micro-nuclei which lie at the edge 

 of or embedded in the macro-nucleus. 



6 Reproduction in Tillina takes place by the formation of 

 division cysts, within which the protoplasm divides to form two 



