ULTRASTRUCTURE OF THE NERVOUS-SYSTEM OF GYRATRIX-HERMAPHRODITUS (TURBELLARIA, RHABDOCOELA) .1. BRAIN

The fine structure of the nerve cells in the brain of Gyratrix hermaphroditus is studied as well as the structure of the neuropile. General features of all nerve cells are a prominent neucleus with a small nucleolus, a scanty layer of cytoplasm containing mitochondria, free ribosomes, few profiles of granular endoplasmic reticulum, smooth endoplasmic reticulum, subsurface cisternae, well developed Golgi complexes, multivesicular bodies and numerous vesicles diagnostic for different nerve cell types. On the basis of the vesicle content four nerve cell types can be distinguished. The following types of vesicles are observed. Dense cored vesicles (50–80 nm), dense vesicles (60–120 nm), small lucent (synaptic) vesicles (40–50 nm), large lucent vesicles (50–200 nm) and lysosome‐like vesicles (200–500 nm). The significance of the variations in the interior electron dense material of the multivesicular bodies is discussed. 1979 The Royal Swedish Academy of Sciences