438 



Mr. T. Goodey. The Excy 'station of 



[Feb. 28, 



organisms appear to rotate and cause digestion of the endocyst whilst still 

 within the confines of the ectocyst, afterwards making their exit from the 

 latter by forcing their way through a rupture in the wall. 



Some free endocysts were tested with iodine in potassium iodide solution 

 but they did not stain, nor was any alteration in colour or shape effected by 

 the addition of 70-per-cent. sulphuric acid to the preparation. This 

 indicates that the endocyst of Gastrostyla steinii is in all probability of the 

 same nature as that of Colpoda cuculhis. 



Note on the Initial Stages of Encystation in Colpoda cucullus. 

 On examining a hanging-drop culture in which Colpoda had been active 

 for two days many organisms were found to be encysting, probably com- 

 mencing to form resting cysts, since there was not an abundance of food. 

 An opportunity therefore presented itself for the study of the earliest stages 

 of encystation. 



Whilst examining under the oil-immersion a group of three rounded 

 Colpoda which were revolving, each within a limiting membrane, a free- 

 swimming Colpoda came into the field. It did not move away but began to 

 revolve, the cilia moved very violently, and the organism began to lose its 

 characteristic form and outline and became more rounded. It appeared as 

 though in this initial stage of encystation some jelly-like substance or 

 mucilage were exuded from the ectoplasm, and that because of this the cilia 

 had great difficulty in moving. They seemed to move in bunches which 

 gave the appearance of waves on the surface of the organism. Shortly after 

 this there was a definite limiting membrane within which the organism was 

 revolving, clearly propelled by means of its cilia, which were easily visible 

 under the oil-immersion. 



This is in accord with Ehumbler's observations. He watched the forma- 

 tion of the cyst membranes in division cysts and resting cysts of Colpoda, and 

 was convinced that rotation within the cyst was due to ciliary activity. 



Summary and Conclusions. 



1. The cyst membranes of Colpoda cumllus consist of the outer ectocyst 

 and the inner endocyst. The ectocyst is insoluble in strong acids, gives no 

 reaction with iodine and strong sulphuric acid, only stains with hematoxylin, 

 is insoluble in alcohol and ether, and is only dissolved by 20-per-cent. 

 caustic soda. In all these properties except the absence of any reaction to 

 iodine, it resembles the outer cyst wall of Euglena viridis, investigated by 

 Butschli, which is composed of a nitrogen-free carbohydrate compound. 



2. The endocyst is composed of a transparent substance which is insoluble 



