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The fine structure analysis of the proboscis teeth in the genus Carcharodorhynchus Meixner and of the proboscis hooks in the genus Diascorhynchus Meixner revealed that these structures are not derived from local cuticularizations of the epidermis, but rather are closely associated with the basement lamina of the proboscis sheath epithelium. In Diascorhynchus the hooks are specializations within the basement lamina enclosing the proboscis. The proboscis teeth in Carcharodorhynchus seem to be either an intracellular differentiation within the modified proboscis sheath epithelium or, as in Diascorhynchus, a derivative of the basement lamina. The latter is supported by the finding of similar, dermal teeth clearly derived from the basement lamina in the body wall of several species of the genus Carcharodorhynchus. It appears from this study that most “cutic‐ular” differentiations of the body wall in Turbellaria are either derivatives of the basement lamina or of the cytoplasm of the epidermis cells. These considerations are discussed in the light of possible evolutionary pathways leading from a ciliated epidermis (e.g. free‐living acoelomates) to a cuticularized hypodermis (e.g. Aschelmimhes and Articulata).

Doe, D. A. (Department of Zoology, University of North Carolina, Chapel Hill, North Carolina 27514, USA.) The proboscis hooks in Karkinorhynchidae and Gnathorhynchidae (Turbellaria, Kalyptorhynchia) as basement membrane or intracellular specializations. Zool. Scr. 5 (3–4): 105–115, 1976.—The fine structure analysis of the proboscis hooks in the genus Cheliplana Beauchamp revealed that these structures are specializations within the basement lamina enclosing the proboscis. The fine structure analysis of the proboscis hooks in the genus Gnatho‐rhynchus Meixner revealed that these structures are intracellular specializations within a fold of epithelium located at the junction of the proboscis sheath and proboscis cone. The electron dense hook material is deposited primarily in microvilli along the outer cell surface of the cone epithelium. The fine structural analysis of the unarmed proboscis in the genus Proschizorhynchus Meixner agrees with the description for the armed schizorhynchs and these findings support the view that the Schizorhynchia is a monophyletic group. The fine structural analysis of the unarmed proboscis in Florianella bipolaris Rieger & Sterrer agrees with the description for Gnathorhynchus. A comparison of the proboscis and hooks in the two kalyptorhynch suborders suggests a more distant relationship between them. A discussion of the methods for the anchorage of intracellular, intercellular and extracellular hard structures is also included.

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