The Ultrastructure of Crithidia fasciculata and Morphological Changes Induced by Growth in Acriflavin*

SYNOPSIS. Crithidia fasciculata is similar to other trypanosomatids in ultrastructure. Of considerable interest is the finding of a lamellar membrane formation attached to the mitochondrion. Some evidence is provided for the tentative hypothesis that this membrane formation is the precursor of mitochondrial membranes. The cellular origin of this structure is unknown. Growth in acriflavin results in a marked alteration of the mitochondrion and kinetoplast. Both structures are deficient in cristae. In addition, the kinetoplast loses its normal fibrillar appearance and becomes a smaller, more electron‐dense organelle. These effects are discussed in relation to the proposed involvement of the kinetoplast in the elaboration of functional mitochondria.