Abstract
A new species of Euplotes, a marine hypotrichous ciliate, found in San Francisco Bay can be readily induced to encyst and excyst at will by the following method.
By means of a micro-mouth pipette, from 25 to 35 organisms picked at random from a thriving culture are placed on a slide or coverslip within a drop of the culture medium. The slide (or coverslip) is then placed in a moist chamber to allow gradual evaporation to take place. The rate of evaporation under these conditions at about 22° C. gives the best results. Within 1 to 10 hours, or even less time, encystment occurs. This process includes a gradual decrease in motility of the organisms until they become fixed to the slide, whereupon they gradually assume a rounded form. External organelles at first can be recognized within the cyst wall but later disappear from view. Excystment takes place when a small drop of fresh culture medium, tap, or distilled water is added to the drop containing the cysts. The time required for complete excystment depends upon the age of the cyst and varies from a few minutes to 1 or 2 hours. A contractile vacuole reappears and functions slowly soon after the addition of water. The cyst wall breaks, usually just above the contractile vacuole. The contents stream to the outside, external organelles make their appearance, and soon the organism again becomes free-swimming.
The above method has proved to be an excellent means for studying the structural changes which occur during cystment. The cov-erslip is inverted upon a depression slide, the edges sealed with vaseline, and now the slide may be placed under a microscope. There the processes of encystment and excystment can be studied with any magnification, including oil immersion.
Get full access to this article
View all access options for this article.