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The Excystation of Colpoda cucullus from its Resting Cysts, and 



the Nature and Properties of the Cyst Membranes. 

 By T. Goodey, M.Sc. (Birm.), late Mackinnon Student of the Royal Society. 



(Communicated by A. D. Hall, F.R.S. Received February 28, — 

 Bead May 8, 1913.) 



(From the Rothamsted Experimental Station, Harpenden.) 



Introduction. — Having had occasion to make use of the resting cysts of 

 Colpoda cucullus in the course of my work on the protozoa of the soil* I was 

 interested by the way in which the organisms escape from the confines of 

 the cyst membranes. The processes involved were by no means obvious on 

 somewhat casual observation, and it became necessary to study them in 

 considerable detail before they could be fully elucidated. Moreover it was 

 thought that by working out as fully as possible the conditions involved in 

 excystation some light might be thrown on the activity or inactivity of the 

 protozoa in the soil. 



The water-content, available food supply, and temperature of any soil are 

 obvious external factors in determining the possibility of protozoal activity, 

 but that these were all the determining factors was by no means clear. 

 There was the possibility that certain peculiar external influences were 

 required for excystation, and if these could be determined it was possible 

 that one would be able to say whether they were present or absent in a soil 

 normally containing protozoa. 



In studying the literature bearing on the subject it was soon evident that 

 although a considerable amount of work had been done by earlier workers, 

 particularly by Rhumblerf on the excystation of Cotyoda and the different 

 kinds of cysts formed by it, and by FabreJ on the properties of cyst 

 membranes, little or no work was recorded dealing with the processes 

 involved in the emergence of active forms from resting cysts. 



I therefore set out to investigate the matter as fully as possible. 



Methods. — The experiments have been carried out in hanging-drop 



* Goodey, T., 'A Contribution to our Knowledge of the Protozoa of the Soil," 'Roy. 

 Soc. Proc.,' 1911, B, vol. 84, p. 165. 



t Rhumbler, L., ' Zeitschr. fiir wissen. Zool.,' 1888, vol. 46, p. 571. 



X Fabre-Domergue, P., "Sur les proprietes dialytiques de la membrane du Kyste des 

 Infusoires,' : 'Compt. Rend.,' 1885, vol. 101; "Recherches anat. et physiol. sur les 

 Inf usoires cilies," ' Ann. des Sci. Nat.' (7 s.), ' Zoologie,' 1888, vol. 5. 



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