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Mr. T. Goodey. A Contribution to our [May 19, 



The foregoing experiments with soils and resting cysts show that, as regards 

 time, the first ciliated protozoa were revealed in soil cultures only after about 

 one and a half hours. This is the shortest time observed, and no ciliated 

 protozoa have been found earlier than this ; as a rule the incubation period 

 is rather longer. The incubation period for the excystation of Col. cucullus 

 from resting cysts is from two to four hours. 



In appearance, the first ciliated protozoa to occur in soil cultures are clear, 

 and have a finely granular protoplasm with a varying quantity of larger 

 granules. They have no food vacuoles, and it is often possible, without 

 staining, to distinguish the nuclear area as a denser region of protoplasm. 

 In one or two cases the meganucleus with its micronucleus has been well 

 seen in Col. cucullus without staining. Especially noteworthy are the three 

 free-swimming, cylindrical vorticellid forms (Plate 4, fig. 11). The ordinary 

 form of Vorticella is stalked and attached, whilst the cylindrical, free-swimming 

 form, without food vacuoles, is characteristic of but recent emergence from a 

 resting cyst. 



Eecently excysted Col. cucullus are easily recognisable by their clear 

 protoplasm, their readily distinguishable nuclear area, and by the absence of 

 food vacuoles. 



(g) Summary and Conclusions. — 1. Given the opportunity for ciliated 

 protozoa to live actively and multiply on the surface of the soil, with the 

 production of resting cysts on the occurrence of conditions adverse to further 

 growth, it is possible to account for the ciliates which develop in soil cultures. 

 The resting cysts produced on the surface would gradually be washed down 

 into the soil, where they would remain. Many of these would, no doubt, lose 

 their vitality after a long time, whilst others would be capable of excystation 

 when once they came to the surface and conditions favourable to their 

 growth prevailed. 



2. The incubation periods observed for the first ciliated protozoa which 

 appear in soil cultures (1-|- to 3 or 4 hours) and for the earliest Colpoda to 

 emerge from resting cysts (2 to 4 hours) are comparable. Comparable periods 

 required for appearance indicate a similarity in the condition of the protozoa 

 at the commencement of the experiment, viz., the encysted condition. 



3. The first Colpoda to occur in soil cultures are very similar in appearance 

 to those which have just emerged from resting cysts. The protoplasm is 

 generally clear, the nuclear area is distinct and easily visible without stain- 

 ing, and no food vacuoles are present. If the Colpoda had been free-living 

 and actively devouring bacteria in the soil, they must certainly have 

 possessed food vacuoles. This indicates that the ciliated protozoa of the 

 soil are present only in the condition of resting cysts. 



