Plate 2

Fig. 1: Ectoderm of the column, stained with mercury/bromphenol blue, × 780.

A, glands cells of type A; B, glands cells of type B.

Fig. 2: Transverse section through column body wall to show mesogloeal fibres. Stained for reticulin by Gordon & Sweet's method, × 1000. EC, ectoderm; M, mesogloea; S, secretion of gland cells of type C and E.

Fig. 3: Section of the mesogloea of the column body wall. Methyl green/pyronin stain; the cytoplasm of mesogloeal cells has stained with pyronin. Arrows show the location of some cells, × 900.

Fig. 4: Basal Portion of verruco-cinclide from section stained by Mowry/PAS/NYS after pepsin. Structures at the level of the nerve net (arrows) stain darkly with Mowry's reagent, × 760.

EC, ectoderm; M, mesogloea.

Fig. 5: Muscle cell from ectoderm of a tentacle of I. olivacea, drawn from a photograph of a dissociation preparation, × 760.

C, muscle fibre; CY, cytoplasm surrounding cell nucleus; S, cytoplasmic strand.