Supposing the water to have become opaque, proceed thus--Draw off a portion into a large jug, and mix with it the diluted acid as before stated, then let the jug remain undisturbed for about twelve hours. The vegetation having been deposited in flakes at the base of the vessel, the water should then be gently strained off through a piece of fine muslin into a second receptacle, which, in its turn, should be allowed to stand for some time, and the contents again strained as before. This process it is advisable to repeat several times, until the whole of the fluid in the tank has been thoroughly cleansed from impurity. Should the water be returned too early, an unpleasant fur coating will appear over the entire base of the tank. This can be easily removed by means of the siphon. Let one end of this instrument, when in action, be passed gradually over the lower portion of the vase, and in the course of a few minutes every sign of 'fur' will be obliterated with the loss of but a small portion of water. When once the fluid has been clarified in the manner here mentioned, there is little fear of the young aquarianist being again troubled in like manner for many months, the acid apparently preventing the algæ from being reproduced to any such excess as hitherto. GLOSSARY OF SCIENTIFIC TERMS. Extracted principally from Professor Owen's learned work entitled, "Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals." =Ambulacra= (L. _ambulacrum_, an avenue, or place for walking). The perforated series of plates in the shell of the Sea-star, or Sea-urchin, through which the sucking-feet are protruded. =Acalepha= (Gr. _akalephe_, a nettle). The class of radiated animals with soft skins which have the power of stinging like a nettle. Commonly called Sea-nettles or Jelly-fish. =Actinæ= (Gr. _aktin_, a ray). The genus of Polypes which have many arms radiating from around the mouth. =Alternate generation.= That modification of generation in which the young do not resemble the parent, but the grandparent; so that the successive series of individuals seem to represent two species, alternately reproduced, in which also parthenogenesis alternates with the ordinary engendering by impregnation. =Algæ= (sea-weeds). A large class of cryptogamic plants inhabiting salt and fresh water. =Anomoura= (Gr. _anomos_, irregular, and _oura_, a tail). A section of crustaceous animals distinguished like the Hermit crabs, by the irregular form of the tails. =Annelid.= The Anglicised singular of _annelleta_. =Adductor muscles=, are those which hold together the shell of a bivalve, such as the Oyster, Mussel, &c. =Animalcules.= Those extremely small animals which are invisible to the naked eye. =Antenna= (from the Latin for yard-arm). Applied to the jointed feelers or horns upon the head of insects and crustacea. =Balanoids= (Gr. _balanos_, an acorn). A family of Sessile cirripeds, the shells of which are commonly called Acorn-shells.