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Protozoa

Place a small handful of dried grass in a jar of boiled rainwater and after a few days life appears to have spontaneously evolved. In reality spores and cysts of organisms exist in the grass and when conditions are favourable they emerge from their suspended animation. The first organisms to appear are bacteria which make their presence felt by turning the infusion cloudy but within a few days the turbidity clears as larger organisms make their appearance and start to feed on the bacterial flora. Many are large enough to be seen with the unaided eye as minute specks drifting through the liquor. They are ciliates, small, unicellular organisms that propel themselves through the water by a mass of short beating hairs or cilia.

One of the first and most frequent inhabitants of such a hay infusion is the Paramecium or Slipper Animalcule. They are often present in vast numbers and will keep many an observer fascinated for hours.

As it moves through the water, particles such as bacteria are coaxed along a groove running down the length of the body by rhythmically beating cilia to a cavity where they are ingested. Imaginatively these are known as the oral groove and cavity.

On this specimen both are clearly shown. Paramecia can travel forward or backward but need to travel forwards when feeding. The broad rounded end is the front. This specimen measures 84um (0.084mm) in length.

An individual cell clearly showing the rhythmic wave motion of the beating cilia that propels it through the water.

As the hay infusion ages, the population of protozoa alters reflecting the different nutritional requirements of the changing species. One of the last to appear is often the Amoeba, often cited in school text books as a single-celled organism resembling a blob of jelly. An apt description perhaps but hardly one to excite the casual observer. A few minutes watching an Amoeba soon gets the observer asking questions.

Amoeba proteus x159 feeding by engulfing food particles
as it lazily meanders over decaying vegetation.