Ultrastructural observations on the erythrocytes and thrombocytes of the tuatara, Sphenodon punctatus (Gray).

The erythrocytes of Sphenodon punctatus (Gray) are nucleated, ellipsoidal and flattened, and contain 55--65 microtubules in their marginal band. The thrombocytes are also flattened, ellipsoidal, nucleated cells and in electron-microscopic preparations occurred in aggregrates. The thrombocytes appeared to be 'activated' and possessed many pseudopodia which were devoid of organelles. The latter were concentrated in the perinuclear region and were encircled by a ring of microtubules. The organelles included ribosomes, mitochondria, membrane--bound dense material and numerous actin-like microfilaments. Cytoplasmic vacuoles contained a moderately dense, filamentous material and/or spheroidal electron-dense inclusions, beta-glycogen particles were scattered in the general cytoplasm and were most concentrated in the pseudopodia. The erythrocytes and thrombocytes of S. punctatus are compared with those in other vertebrates.