The Fine Structure of Colpoda maupasi with Special Emphasis on Food Vacuoles*

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Abstract
SYNOPSIS. An electron microscope study of Colpoda maupasi Enriques, isolated from the intestine of the blue‐tongued skink Tiliqua nigrolutea, showed that the fine structure of this ciliate is similar in all respects to that of free‐living ciliates. The correspondence applies particularly to the structure, distribution and number of mitochondria. This organelle has a rich intramitochondrial structure in the form of microvilli; it is found close to the periphery, near the nuclear apparatus and in other parts of the cytoplasm. It was concluded that the association between Colpoda maupasi and Tiliqua nigrolutea was probably accidental and limited to the cyst stage. Thus electron microscopy confirmed a conclusion arrived at by light microscopy.The presence of numerous food vacuoles made it possible to study stages of digestion within this organelle. Four major types of food vacuole were distinguished. Type 1 food vacuoles are characterized by their large size, the presence of intact bacteria and abundance of water. In type 2 the food vacuole is deprived of water, the bacteria are pressed together and the nuclei have lost their structure. Type 3 food vacuoles contain only bacterial ghosts, cytoplasmic and nuclear material having been digested. Food vacuoles of this type are found only occasionally, suggesting their short duration. It is of interest that during this transient stage the bulk of digestion takes place. In type 4 nothing reminiscent of bacteria is found; there are only myelin figures and vesicles of different sizes. Evaginations and invagnations of the vacuolar membrane and vesicles of different size and structure inside and outside the food vacuoles of types 1, 3 and 4 suggest that extensive communication exists between the cytoplasm and the food vacuole. It seems likely that enzymes are delivered to the food vacuole and digested materials are released from the food vacuole to the cytoplasm.