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132 SPONTANEOUS GENERATION.conclusively demonstrated by Messrs. Dallinger and Drysdale, in theiraccounts of the life-history of various species of monads, contributed chieflyto the 'Monthly Microscopical Journal' during the years 1873 to 1875, andas described hereafter, systematically, under the specific headings of MonasDallingeri, Cercomonas typica, and Heteromita rostrata and uncinata. Asthere recorded, the spores or germs of these animalcules, when first releasedby the rupture of their enclosing cyst,, are of such extreme minutenessas to defy individual resolution with a 3Vinch objective and associatedmagnifying power of no less than 15,000 diameters, appearingin theaggregate under such conditions as a faintly granular fluid, having a refractiveindex scarcely distinguishable from the surrounding water. Asgermination and development progress, each individual spore, however,passes within the range of vision, and by degrees assumes the determinatesize, form, and characteristics of the parent organism. The record ofthese reproductive phenomena of the monads in question was broughtforward at the time simply as a newly discovered and interesting chapterin their life-history. Later on, however, Mr. Dallinger published in thethe results of his'Monthly Microscopical Journal' for December 1876,further investigations of these minute organisms, in which, through correlatinghis own discoveries with those of Professor Tyndall, he obtainedsome most important results.Drying up the residual portion of a maceration or infusion containing acertain known form of monad, he had already shown that the light, porous,papier-mache-like substance resulting from such desiccation might besaved, like the seeds of a plant, and used for propagating the species atwill inany suitable sterilized putrescible fluid. Working on this basis,an infusion of haddock's head, containing in abundance the so-called" Springing Monad" (Heteromita rostrate?) and the Calycine Monad (Tetramitusrostratus) in the spore-producing stage, was gradually evaporated,then raised to a temperature of 150 Fahr., or 10 above that required tokill the adult form, and so reduced to a porous and highly friable condition.A small portion of this dried material, reduced to powder, was now diffusedin an experimental chamber like those employed by Professor Tyndall,and the condensed beam of an oxyhydrogen lime-light being transmittedthrough the windows, its path within the chamber was more brilliantlymarked than on the outride, indicating the preponderating existence thereinof the spore-containing or germinal dust. This was now allowed to settlefor a space of four hours and a half, when the lime-light still demonstrated,though in a less marked manner, the presence of the suspended dust. Tensmall glass dishes, each partially filled with a sterilized fluid, were thenintroduced into the chamber, four of them being covered with projectingglass lids, mechanically movable, without opening the door of the chamber,and smeared with glycerine, to prevent the disturbance of any previouslysettled germs. At. the end of twenty-four hours the lids were removedfrom the four covered vessels, and the whole now left undisturbed for