=Exuvium=, Pl. =exuviæ= (L. _exuo_, I cast off). The shell or skin of an animal which is shed in moulting. =Epizoa= (Gr. _epi_, upon; _zoon_, an animal). The class of low organized parasitic crustaceans which live upon other animals. =Fissiparous= (L. _fissus_, divided; _pario_, I produce). The multiplication of a species by the self-cleavage of the individual into two parts. =Frond= (L. _frons_, a leaf). A term applied to that part of flowerless plants resembling true leaves. =Fucivorous= (L. _fucus_, sea-weed; _voro_, I devour). Animals which subsist on sea-weed. =Flora.= The plants which belong to a country or district. =Foliaceous= (L. _folium_, a leaf). Shaped or arranged like leaves. =Gasteropoda= (Gr. _gaster_, stomach; _pous_, a foot). That class of animals which (like the Snail) have the locomotive organ attached to the under part of the body. =Gemmiparous= (L. _gemma_, a bud; _pario_, I produce). Propagation by the growth of the young like a bud from the parent. =Habitat.= The locality in which an animal habitually resides. =Hinge.= That part of a shell at which the valves cohere. =Hyaline= (Gr. _hualos_, crystal). The pellucid substance which determines the spontaneous fission of cells. =Hydra= (Gr. _hudra_, a water serpent). The modern generic name of certain fresh water polypes. =Hydrogen= (Gr. _hydor_, water; _gemmæ_, I produce). A gas forming one of the components of water and atmospheric air. =Infusoria.= The class of animalcules which abound in vegetable and animal infusions. =Lamellibranchiata= (L. _lamella_, a plate; _branchiæ_, gills). The class of acephalous molluscs, with gills in the form of membraneous plates, of which the oyster and mussel are familiar examples. =Larva= (L. _larva_, a mask). Applied to an insect in its first active state, which is generally different from, and, as it were, masks the ulterior form. =Ligament=. A membrane close by the hinge which connects the valves. =Mantle.= The external soft, contractile skin of the mollusca, which covers the viscera and a great part of the body like a cloak. =Macroura= (Gr. _makros_, long; _oura_, a tail). A tribe of ten-footed crustacea (as the Lobster, Cray-fish), which have long tails. =Medusæ.= A genus or family of soft radiated animals or Acalephæ, so called because their organs of motion and prehension are spread out like the snaky hair of the fabled medusa. =Molecules.= Microscopic particles of matter. =Mollusc--Mollusca= (L. _mollis_, soft). The primary division of the animal kingdom. It contains most shell-fish, slugs, &c. =Monograph= (Gr. _monos_, one; _grapho_, I write). A written description of a single thing, or class of things. =Multivalve= (L. _multus_, many; _valvæ_, folding doors). Shells composed of many pieces or valves, as the Chiton. =Nudibranchiate= (L. _nudus_, naked; _branchiæ_, gills). An order of gasteropods, in which the gills are exposed, as the Eolis, Doris, &c.