The structure of opalinids, as revealed by the technique of micro‐incineration

Opalinids from the rectum of Rana pipiens were isolated in large numbers and fixed in a mixture of nine parts of absolute alcohol and one part of neutral formalin. These were embedded in paraffin and incinerated according to the technique of Policard. Examination of the preparations by dark‐field illumination showed that the micro‐incinerated protozoa retained their distinctive morphological and cytological characters, for the mineral ash had the same topographical distribution as the cell inclusions in the control stained preparations. The coarse vegetative granules of the cytoplasm were preserved as distinct masses of ash which corresponded exactly to these bodies in the control preparations. The structure of the myonemata and the cilia was perfectly preserved. The chromatin material of the nucleus, more or less abundant, left little or no ash, which is quite in contrast to the findings of Scott with regard to amphibian and mammalian nuclei.