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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.