Plate 1

Fig. 1: The column body wall of I. olivacea. A transverse section stained by the Mallory/Azan technique, × 460.

C, muscle fibre; EC, ectoderm; EN, endoderm; M, mesogloea; N, ectodermal nerve net; arrows show mesogloeal cells.

Fig. 2: Supporting cell from the ectoderm of the column. Dissociation preparation photographed by phase contrast illumination, × 620. N, nucleus; P, projection.

Fig. 3: Transverse section of the column showing the outer region of the ectoderm. Heidenhain's iron haematoxylin/orange G stain, × 930. C, cuticle; P, projections.

Fig. 4: Epitheliomuscular cell from the endoderm of the column. Dissociation preparation photographed by phase contrast illumination, × 1,100.

C, muscle fibre; F, flagellum; S, cytoplasmic strand connecting muscle fibre to epithelial part of cell (Nucleus not showing).

Fig. 5: "Verruco-cinclide" from a transverse section of the column.

Mallory/Azan preparation, × 490.

EC, ectoderm; EN, endoderm; M, mesogloea.

Fig. 6: Transverse section through column body wall showing orientation of mesogloeal fibres. Sulphation toluidine blue stain, × 740.

C, muscle fibre; EC, ectoderm; M, mesogloea.

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.

Plate 3

Fig. 1: Longitudinal section through endoderm of body wall, showing gland cells. Mowry colloidal iron/PAS/NYS stain. Photographed through a deep blue filter to emphazise the PAS staining of type "2" gland cells (arrowed), and the NYS positive type "1" gland cells (P) × 500. C, coelenteron; E, endoderm.

Fig. 2: The same section as Fig. 1, but photographed through a red filter to emphasize the Mowry colloidal iron positive type "3" gland cells (arrows), × 500.