Amoeba was discovered by

The correct option is Rosenhof.

Step-by-step Explanation:

1. Discovery of Amoeba:
The microscopic organism known as Amoeba was first discovered by the German naturalist and miniature painter August Johann Rösel von Rosenhof in the year 1755.
In his publications, he referred to the organism he observed as "der kleine Proteus" (the little Proteus), named after Proteus, the shape-shifting sea god of Greek mythology, due to the organism's constantly changing body shape.

2. Later Naming:
The name Amoeba was subsequently given to the genus by Bory de Saint-Vincent in 1822, derived from the Greek word amoibè, which means change.

3. Analyzing the Options:
- Rosenhof (August Johann Rösel von Rosenhof) is the correct scientist credited with the discovery of the amoeba.
- Other options like Jenner (famous for the smallpox vaccine) and the remaining names are not associated with the initial discovery of this unicellular organism.