Plate 1

Fig. 1: A hydranth of S. tenella, from life, as seen under dark field illumination, × 100.

A, M, B, regions corresponding to the apical, middle and basal regions, respectively, seen in longitudinal sections of hydranths; G, developing gonophore; H, hydrocaulus; T, tentacle.

Fig. 2: Transverse section through apical hydranth region. Note villated endoderm with gland cells situated at periphery of villi. PAS/AB/NYS stain, × 410.

EN, endoderm; G, gland cells.

Fig. 3: Longitudinal section through basal hydranth region. Note columnar ectodermal cells, and vacuolated endodermal cells. Many endodermal cells contain food vacuoles. Mallory/Azan stain, × 1,000.

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

Fig. 4: Transverse section of hydranth in apical region to show cuticle hanging from ectoderm. Mallory/Azan stain, × 1,000.

C, cuticle; EC, ectoderm; M, mesogloea; T, tentacle base.

Fig. 5: Transverse section of ectoderm and mesogloea in apical region, showing small cells (arrows) considered to be interstitial cells. Delafield's haematoxylin and eosin preparation, × 1,000.

EC, ectoderm; M, mesogloea; N, nerve cell; NU, nuclei of epitheliomuscular cells.

Fig. 6: Longitudinal section of hydrocaulus at base of hydranth, stained with PAS/haematoxylin. The perisarc, mesogloea, and ectodermal cell granules stain intensely with Schiff's reagent, × 2,000.

EC, ectoderm; M, mesogloea; P, perisarc.

Fig. 7: Longitudinal section of hydranth in apical region showing nerve cell at base of ectoderm with nerve process crossing mesogloea to endoderm. Heidenhain's iron haematoxylin stain, × 1,000.

EC, ectoderm; EN, endoderm; N, nerve cell.

Fig. 8: An endodermal epitheliomuscular cell from a dissociation preparation. The flagellum is not visible. Phase contrast photomicrograph, × 700.

M, myoneme; N, nucleus.

Plate 2

Fig. 1: Longitudinal section of hydranth body wall. Specimen fixed in Formol/Calcium, stained with Mallory/Azan. Nerve cells (arrowed) show clearly. Note cuticle, and densely staining food vacuoles in endoderm. × 1,100.

C, cuticle; EC, ectoderm; EN, endoderm.

Fig. 2: Region of ectoderm adjacent to that shown in Pl. 2, Fig. 1, from the same preparation. Note hair like processes extending from sensory cell, × 1,650.

EC, ectoderm; M, mesogloea; S, sensory cell.

Figs. 3A, 3B: Transverse serial sections through body wall of middle hydranth region. Methyl green/pyronin stain, without (A) and with (B) prior RNase digestion, × 1,130.

D, digestive cell; EC, ectoderm; EN, endoderm; M, mesogloea.

Figs. 4A, 4B: Longitudinal serial sections through hypostome. PAS test, with (A) and without (B) prior diastase digestion. Many darkly staining bodies have been removed from the ectoderm and endoderm by diastase digestion. Those remaining represent hypostomal gland cells, × 830.

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

Fig. 5: Longitudinal section of hydrocaulus at hydranth base to show 2-layered structure of perisarc. Mallory/Azan stain, × 1,130.

EC, ectoderm; P1, outer perisarc layer; P2, inner perisarc layer.

Plate 3

Figs. 1A and 1B: Tangential section of hydranth body wall, Mallory/Azan stain. Fig. 1A photographed through a deep blue filter; note densely coloured myonemes of ectodermal cells (MY), and lightly coloured mesogloea (M). Fig. 1B, same section photographed through red filter; mesogloea colours deeply because it is stained with aniline blue; myonemes not clearly seen, × 1,050.

EC, ectoderm; M, mesogloea; MY, myonemes.

Fig. 2: Longitudinal section of middle region of hydranth body wall, showing digestive cells, × 1,000. Delafield's haematoxylin and eosin stain.

D, digestive cell; EC, ectoderm; EN, endoderm; M, mesogloea.

Figs. 3A, 3B: Longitudinal section of mouth region. PAS/AB/NYS stain. Fig. 3A photographed through deep blue filter to emphasize the gland cells which stain with Schiff's reagent. Fig. 3B photographed through red filter to emphasize the gland cells which stain with AB. × 720.

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

Fig. 4: Whole mount of hydrocaulus beneath polyp, photographed by phase contrast microscopy. Soft tissues were removed with a weak "Janola" solution. Note the numerous nematomysts (arrows), × 625.

Plate 4

Fig. 1: Longitudinal section of tentacle. Delafield's haematoxylin and eosin preparation, × 1,000.

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

Fig. 2: Transverse section of a tentacle near its base. The endodermal cells appear radially arranged, around a central cavity. PAS/AB/NYS stain, phase contrast photomicrograph, × 900.

EC, ectoderm.

Fig. 3: Longitudinal section of distal region of tentacle, showing endodermal cells containing food vacuoles (arrows). Mallory/Azan stain, × 1,100.

EC, ectoderm.

Figs. 4A, 4B: Transverse section of hydranth body wall and tentacle base.

PAS/Mowry colloidal iron stain. Fig. 4A photographed through green filter to emphasize the Schiff staining of the mesogloea. Fig. 4B photographed through red filter to show mesogloeal regions which stain blue (these show darkly in the photograph). Note the folding of the cuticle in Fig. 4A. × 750.

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

Fig. 5: Longitudinal section of hydranth body wall in middle region.

Animal fixed without anaesthetization after a period of starvation. Note buckling of mesogloea (M), and aggregates of small dark bodies (arrow) in vacuolated endodermal cells. PAS/AB/NYS stain, × 1,000.

D, digestive cell; EC, ectoderm; EN, endoderm; M, mesogloea.

Figs. 6A & 6B: Nematocysts from dissociation preparations photographed by phase contrast illumination, × 1,000.

Plate 5

Figs. 1A & 1B: Oblique section through polyp base. PAS/Mowry colloidal iron stain, × 1,100. Fig. 1A photographed through deep blue filter to emphasize the Schiff-staining cuticle. Fig. 1B photographed through red filter to emphasize the Mowry colloidal iron-staining outer perisarc layer and ectodermal granules.

C, cuticle; EC, ectoderm; EG, ectodermal granules; EN, endoderm; EP1, cut edge of outer perisarc layer; M, mesogloea; P1, outer perisarc layer; T, tentacle.

Fig. 2: Longitudinal section of hydrocaulus in region of annulations beneath a polyp. PAS/Mowry colloidal iron stain, photographed by Nomarski interference illumination, × 900.

EC, ectoderm; EN, endoderm; M, mesogloea; P1, outer perisarc layer; P2, inner perisarc layer.