Freeze-drying methods for the scanning electron-microscopical study of the protozoon Spirostomum ambiguum and the statocyst of the cephalopod mollusc loligo vulgaris

Abstract

The present study concerns methods of preparing ciliated surfaces for direct examination in the scanning electron microscope. Air-drying methods provide good results with some ciliated structures but do not always preserve the cilia of ciliated protozoons, although the pellicle is well preserved. Air-drying is not suitable for certain epitheia because considerable shrinkage and tearing occur. Freeze-drying methods, with or without pre-fixing, are described. These preserve the cilia in the protozoon Spirostomum in a fairly life-like position. There are some differences in the appearance of unfixed and fixed freeze-dried material--for example, the peristomial membranelles are not seen in the unfixed material. Freeze-drying again proved to be a better method of preparing the sensory epithelium lining the statocyst of the cephalopod mollusc Loligo, because it was successful in preventing the distortion due to shrinkage. The number of hair cells, their orientation, and the area covered by the cells was determined for the macula. The crista was found to be asymmetrical.