1911.] 



Knowledge of the Protozoa of the Soil. 



177 



(f ) Excystation* — Concurrently with the above experiments with soil, a 

 series on the development of free-swimming ciliated protozoa from their 

 resting cysts have been carried out. These have been done chiefly with the 

 cysts of Colpoda cucullus. 



Khumblerj- speaks of obtaining active Col. cucullus by excystation [from 

 " dauercysten " in about six hours. It became necessary, therefore, to 

 determine the length of time required for the excystation of Col. cucullus. 



A supply of resting cysts was obtained from the sides of a flask containing 

 an old culture of this ciliate, and a large number of these cysts were slowly 

 air dried on a filter paper. Undried cysts have also been used. The 

 experiments have been conducted chiefly in hanging drop cultures, either 

 over cavity slides or glass rings, and incubation has in all cases been carried 

 out at 30° C. 



During excystation the outer wall of the cyst, ectocyst, which is generally 

 rather rough and is very resistant, ruptures and permits the transparent- 

 walled endocyst to come out. "Within the latter the organism begins to 

 rotate, and it is seen that the contractile vacuole begins to pulsate. The 

 endocyst gradually swells up and its wall gets thinner and thinner (Plate 4, 

 fig. 5). During this process, the cilia of the Colpoda are moving rapidly, 

 causing it to revolve within the endocyst, and setting in constant motion the 

 mass of defalcated excretory matter extruded during encystation. Finally 

 the endocyst wall gives way and the organism swims away freely. 



The protoplasm is generally finely granular in appearance, and in the 

 endoplasm there are varying quantities of larger granules. Sometimes 'the 

 latter are quite large and rather dark in appearance. 



It is almost always possible for one to distinguish quite easily the situation 

 of the meganucleus as a spherical area, more dense in appearance than the 

 rest of the protoplasm. 



There are, of course, no food vacuoles in the endoplasm, for these are only 

 found after the organism has been obtaining food for some time. 



No. 1. — Col. cucullus emerged in 4 nr. from dried cysts. 

 „ 2. — Col. cucullus emerged in 4j hr. from dried cysts and in 6j hr. from undried cysts. 

 „ 3. — Many Col. cucullus emerged in 3 hr. 25 m. from dried cysts. 

 „ 4. — One or two Col. cucullus emerged in 3j hr. from undried cysts. 

 „ 5. — One Col. cucullus emerged in 2 hr. 35 m. from dried cysts which had been standing 

 on a filter paper moistened slightly with hay infusion on the previous evening. 

 „ 6.— One Col. cucullus emerged in 2 hr. from cysts treated as in 5, only moistened for 

 about 30 hr. with hay infusion. 



* This word is used to designate the stages up to and including the emergence of active 

 protozoa from their resting cysts. 



t B humbler, L., 'Zeitschr. fur wissen. Zool.,' 1888, vol. 46, p. 571. 



