EPIDERMAL. Gr. _epi_, upon; _derma_, skin. Relating to the outer layer of skin. As applied to colour, surface pigment as distinct from hypodermal, or deep-seated colour. GASTROVASCULAR CANAL. Gr. _gaster_, belly; Lat. _vasculum_, a little vessel. The canals or vessels in the umbrella (_manubrium_) of hydrozoa. GONIDIA. Gr. _gonos_, offspring; _oidos_, like. Reproductive bodies in Sea-anemones. HYDRANTH. Gr. _hudor_, water; _anthos_, flower. The bodies or polypes of hydroids which exercise nutritive functions. They were called polypites by Huxley. HYDROPHYLLIA. Gr. _hudor_ and _phyllon_, a leaf. Leaf-like organs protecting the polypites of hydrozoa. HYDROSOMA. Gr. _hudor_ and _soma_, body. The entire organism of a hydrozöon. HYPODERMAL. Gr. _hypo_, beneath; _derma_, skin. In colour, such as lies beneath the surface, as distinct from epidermal. LYTHOCYSTS. Gr. _lythos_, stone, _kystis_, a bladder. Sense organs in hydroids, consisting of transparent capsules inclosing round transparent concretions. MANUBRIUM. Lat. a handle. The central polypite suspended from the interior of the umbrella of hydroids. MESODERM. Gr. _mesos_, intermediate; _derma_, skin. The middle layer of sponges, &c. MESOTHORAX. Gr. _mesos_ and _thorax_. The middle division of the thorax in insects, carrying the second pair of legs. PERISTOME. Gr. _peri_, about; _stoma_, a mouth. The area surrounding the mouth in sea-anemones. PNEUMATOCYST. Gr. _pneuma_, air; _kystis_ a bladder. The air-sac contained in the pneumatophore, see below. PNEUMATOPHORE. Gr. _pneuma_; _phero_, to carry. The float of certain hydrozoa (_Physophoridæ_.) POLYPITE. Gr. _polus_, many; _pous_, foot. The separate animal or zöoid of a hydrozöon. _See_ HYDRANTH. PROTOPLASM. Gr. _protos_, first; _plasso_, I mould. The jelly-like matter which forms the basis of all tissues. It is identical with the _sarcode_ or flesh of protozoa. SAC. Lat. _saccus_, a bag, a small cell. SARCODE. Gr. _sarx_, flesh; _eidos_, form. The protoplasm of protozoa, &c., which see. SPADIX. Lat. _spadix_, a broken palm branch. In zoology a hollow process occupying the axis of the generative buds of hydrozoa. SPOROSAC. Gr. _spora_, a seed, and _sac_. The body containing the ova of hydrozoa. SOMATIC FLUID. Gr. _soma_, the body. The fluid which contains digested food, and taking the place of blood, circulates through the body of hydrozoa. TENTACLES. Lat. _tentaculus_, a little arm. The arms or prehensile organs of Sea-anemones, &c. THREAD CELLS. Cells containing an extensible microscopic thread, possessing stinging properties, common among the _Coelenterata_. THORAX. Gr. a breastplate. The chest. INDEX.