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During the growth of Patellina corrugata's test platelike structures are formed showing typical characters of Hopper-crystals. These features indicate conditions of test development comparable to inorganic skeletal crystal growth. The whole test therefore can be regarded as a skeletal crystal (Hopper-crystal). Skeletal crystal growth is considered to be the basis of morphogenesis in the single-crystal test of Patellina.

Three methods usually applied in preparing biological material for the scanning electron microscope were tested by the investigation of two species of amoebae with different content of water (Amoeba proteus, Vannella simplex). Air drying resulted in both the production of cell shrinkage and cell distortion. When the specimens were dryed from media with increasing vapour-pressure, more satisfactory preservation of surface structures could be obtained. The sequence of potency was: Ethanol, chloroform, isopentane, ethyl ether, freon 11 and freon 13. Short drying periods proved to be more favourable than long ones. Critical-point drying provided much better details of cell surface morphology in both amoebae species. However, some arteficial changes were still detectable as small breaks and destruction of the mucous layer. They must be attributed to the fixation and dehydration procedure. Freeze drying turned out to be superior to both air drying and critical-point drying. Specimens prepared by this method showed no visible differences in cell surface morphology compared to living cells. As a consequence of the relatively high content of water the preparation of A. proteus was more difficult than that of V. simplex.

In 1973 one of the present authors described a new method of cytological observation based upon flattening of living cells. This method was tested with several microorganisms as bacteria, fungi and algae. The application of the method allows the clear resolution of cytological structures that are otherwise obscured or can hardly be recognized. In addition cellular motion and development can be followed much better than by usual methods of cell culture. In certain objects (yeasts and fungal hyphae tips) all cellular organelles are forced into one plane of focus and are thus resolved simultaneously even at highest magnification. Different species especially among the yeasts exhibited quite varying intracellular contrast of mitochondria.