. Structure of Hormiphora: i. Hormiphora is pear-shaped, glossy, transparent, about 5-20 mm in From the opposite sides of the broad or aboral end, project two long, solid tentacles; a. The tentacles bear numerous lateral branches containing adhesive cells and b. Are completely retractile into deep sheaths. iii. Mouth, a slit-like opening present at the narrow oral end.  iv. Eight ad-radially arranged, equidistant meridional bands, the comb-ribs or costae or swimming plates, starting from near the aboral pole and extending about two-thirds of the distance towards the oral pole are present on the surface. These help in swimming. a. A row of transversely arranged comb-­like structures of narrow plates, frayed at their outer ends constitute a comb-rib. b. The COMBS are formed by the fusion of rows of cilia at their proximal ends. v. An aboral sense organ is present in the depression at the centre of the aboral pole. 2. Enteron or Gastro Vascular System of Hormiphora: a. The mouth leads to a flattened tube, the stomodaeum, which functions as stomach and extends to about two-thirds towards the aboral pole. b. The walls of the stomodaeum are pro­vided with internal ridges. 4. The Nervous System of Hormiphora:Sense Organ in Hormiphora: a. Two narrow areas of CILIATED epithe­lium, the polar plates, are present in a de­pression at the centre of the aboral pole. b. Four equidistant groups of very large S-shaped cilia, united to form as many springs, supporting a mass of calcareous particles, arise from the depression. C. A pair of ciliated grooves from each spring run outwards and reach the swim­ming plates of the quadrant. d. The calcareous mass with its springs is enclosed in a transparent case, formed of coalesced cilia. 7. Development of Hermiphora: i. The zygote undergoes cleavage and eight micromeres and eight macromeres are formedii. The micromeres give rise to ectoderm and the macromeres are the source of endo­derm. iii. The micromeres divide rapidly, over­spreads the macromeres, producing an em­bryo, having a central mass of large cells with yolk, partly surrounded by a layer of small cells, incomplete below. iv. The endoderm cells multiply, invagina­tion starts and a gastrula formed by epiboly and emboly, without an archenteron. v. Stomodaeum is formed by invagination of the ectoderm, while the gastro vascular cavities arise by rapid multiplication of endo­derm cells. vi. The gelatinous mesoglea appears be­tween the ectoderm and endoderm. The cells of the mesoglea are ectodermal in ORIGIN. VII. The complex canal system of the adult appears. viii. The swimming plates develop from bands of rapidly dividing ectoderm cells. ix. The tentacles and their sheaths are derived from ectodermal thickenings on each side. x. The muscle fibres and the calcareous bodies of the sense organs develop and the young hormiphora is formExplanation: