Fig. 7

Histology, A,C,E Azan 5 μm sections, B,D: semi- thin, Toluidine-blue, 1 μm. A,B,D: Owenia fusiformis; C: Myriowenia sp.. a: Ventro- lateral part of brain ring. Pigmented cells (pc), which indicate eyes, are located between the epidermal cells. The brain (br) is interwoven by rectangular arranged radial glia cells (gc) which are attached to the basal lamina (bl). Somata (so) of the neurons are located underneath the epidermal cells (epc). b: A stomatogastric plexus (sgp) innervates the digestive system. Dorsal to the medullary cord (mc) a small rim (ri) is present. A cluster of purple colored gland cells (glc) of unknown function opens into this rim. bl: basal lamina of epidermis; mu: musculature; c: The brain (br) of Myriowenia sp. is interwoven by radial arranged glia cells which contain intermediate filaments (if). Somata of the nerve cells (so) are located underneath the epidermal cells (epc). bl: basal lamina. d: Same position as A. Pigment cells (pc) of the eye are arranged in a row. The brain (br) is located underneath the cells. cu: cuticle. e: Posterior part of specimen. In Owenia fusiformis, a lateral located rim is visible from the posterior part of the brain on extending posteriorly. Ciliation (ci) of these cells is more prominent than in the surrounding epidermal cells (epc). Cells (arrows) of the rim are lesser voluminous than in the remaining epidermis; the rim does not contain glands. A nerve plexus (npl) is located at the base of these cells