1911.] 



Knowledge of the Protozoa of the Soil. 



179 



4. Soils stored under conditions very favourable to bacterial activity, and 

 presumably to protozoal activity, if such is possible in the soil, give every 

 indication that the first ciliated protozoa to occur in cultures have developed 

 from resting cysts. Moist soil fresh from the field only yields ciliates slowly. 



The first Colpoda to appear from the soil to which they had been added 

 in active condition, only occur after sufficient time has elapsed for emergence 

 from resting cysts. The protoplasm resembles that of recently excysted 

 Colpoda. These facts indicate that the free-living organisms added to the 

 soil had not remained in the active condition, but had encysted. 



General Conclusion. — The ciliated protozoa which are so characteristic 

 a feature of cultures made from soil only exist in the soil in an encysted 

 condition. In consequence, they cannot function as the factor limiting 

 bacterial activity in the soil. 



From the nature of the methods employed in the galvanotaxis experiments 

 it is only possible, as yet, to deal with ciliated protozoa ; amoebae and 

 flagellates are not dealt with. For this reason the inferences drawn only 

 -apply to ciliates. 



In conclusion, I desire to offer my best thanks to Mr. A. D. Hall, and to 

 the Lawes Agricultural Trust, for the facilities afforded me to carry out the 

 work at this station. Especially grateful am I to Dr. H. B. Hutchinson, 

 with whom I have been intimately associated during the course of the work, 

 for the unfailing assistance which he has given me, both by suggestion and 

 criticism. To Prof. F. W. Gamble I should also like to express my thanks 

 for bringing me into touch with the work and for much valuable criticism. 

 I am also indebted to the Birmingham Natural History and Philosophical 

 Society for a grant from the " Endowment of Eesearch Fund." 



LITEEATUEE. 



1. Biitschli, 0., Bronn's 'Klassen des Thier-reichs, Protozoa,' 1889. 



2. Dobell, C. C, "The Structure and Life History of Copromonas svMUis," 'Q. J. Micr. 



Sci.,' 1908, vol. 52, p. 75. 



3. Dofiein, F., ' Lehrbuch der Protozoenkunde,' Jena, 1909. 



4. Enriques, P., "Sulla Morfologia e Sistematica del Genere Colpoda," 'Arch, de Zool.,' 



4th Series, p. 8 ; ' Notes et Eevue,' p. 1. 

 -5. Hickson, S. J., in 'A Treatise on Zoology. Part 1. — Protozoa,' 1st and 2nd Fascicles, 

 1903 and 1909. 



6. Kent, S., 'A Manual of the Infusoria,' London, 1880—1882. 



7. Kiister, E., ' Kultur der Mikroorganismen,' Leipzig, 1907. 



8. Maupas, E., "Contrib. a, l'etude morph. et anat. des Infusoires cilies," 'Arch, de 



Zool.,' 1883, 2nd Series, vol. 1, p. 427. 



