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I 1 6 ORGANIZATION OF THE INFUSORIA.on the more remote objects in the microscopic field, while it may be cutwith the scissors to any required -size or shape.In the investigation of the Flagellata, or indeed of any Infusoria inwhich it issought to arrive at an accurate knowledge of the life or developmentalhistory of any given type,it is desirable that the same individualzooid or animalcule should be continuously examined. An importantmechanical obstacle that has to be overcome in the conduct of such continuousinvestigation, which may extend over many hours or days, resultsfrom the rapid evaporation of the water or other fluid from beneath thecovering glass, combined with the necessity of keeping it constantlyreplenished. Various mechanical appliances for accomplishing the desiredend have been introduced by Recklinghausen, Leuckart, and other Continentalworkers, none of these, however, being equal in efficiency to thatemployed by Messrs. Dallinger and Drysdale, during their famous" Researches into the Life-history of the Monads," figured and described inthe 'Monthly Microscopical Journal' for March 1874. The illustrationsgiven of this apparatus with accompanying explanations are reproducedin the plate devoted to mechanical appliances at the end of the atlas tothis volume, and may be thus briefly described. It consists firstly ofa plain glass stage, about the one-tenth of an inch thick, fitted so as toslide on in place of the ordinary sliding stage of the microscope. Fromthe left-hand anterior border of this stage a projecting arm is producedwhich carries a socket for the reception of a small glass reservoir aboutI \ or 2 inches deep. The glass stage being too thick to work through withan achromatic condenser and high powers, a circular aperture of sufficientsize is cut through it,and a piece of thin glass cemented on its uppersurface. A piece of blotting-paperis now cut coinciding in form with theglass stage, but slightly smaller, and with a tongue-like projection that liesalong the projecting arm and dips down into the glass reservoir. Acircular aperture of larger size than the covering glass employedis cutout of the centre of this paper, such aperture,made use of, being preferentially the \\ of an inch.where a -inch cover isThe foundation of themoist chamber is now complete, and itonly remains to provide thebounding walls. This Messrs. Dallinger and Drysdale accomplish bymeans of a piece of glass tubing, about i^ inch in diameter, cut to f inchin length. Across one end of this tubinga thin sheet of caoutchouc isnext firmly stretched and securely tied, and a small hole perforated in itscentre. The tubing with its free edge, which should be carefully ground, isnow placed concentrically upon the glass stage, over the aperture in theblotting-paper, and the object-glass racked down upon the perforation inthe caoutchouc. The caoutchouc should be sufficiently thin to offer noimpediment to the action of the fine adjustment, while it at the same timeclasps the object-glass firmly round its central perforation and in combinationwith the lowermost or free edge resting on the blotting-paper, constitutes apractically air-tight chamber. Everything is now in working action and it