. The microscope and its revelations. one individual. In the1 Monthly Microscopical Journal, vol. vi., 1871, p. 71. 6l8 MICROSCOPIC FORMS OF VEGETABLE LIFE--THALLOPHYTES genus Mastogloia, which is specially distinguished by having theannulus furnished with internal cost* projecting into the cavity ofthe frustule, each frustule is separately supported on a gelatinouscushion (fig. 465, B), which may itself be either borne on a branchingstipe (A), or may be aggregated with others into an indefinite mass(fig. 466). The careful study of these composite forms is a matterof great importance, since it
. The microscope and its revelations. one individual. In the1 Monthly Microscopical Journal, vol. vi., 1871, p. 71. 6l8 MICROSCOPIC FORMS OF VEGETABLE LIFE--THALLOPHYTES genus Mastogloia, which is specially distinguished by having theannulus furnished with internal cost* projecting into the cavity ofthe frustule, each frustule is separately supported on a gelatinouscushion (fig. 465, B), which may itself be either borne on a branchingstipe (A), or may be aggregated with others into an indefinite mass(fig. 466). The careful study of these composite forms is a matterof great importance, since it enables vis to bring into comparisonwith each other great numbers of frustules which have unquestionablya common descent, and which must therefore be accounted as of thesame species, and thus to obtain an idea of the range of variationprevailing in this group, without a knowledge of which specific defi-nition is altogether unsafe. Of the very strongly marked varietieswhich may occur within the limits of a single species, we have an. PIG. 464.—Schizonema Grevillii: A, natural size ; B, portion magnified fivediameters; C, filament magnified 100 diameters ; D, single frustule. example in the valves C, D, E, F (fig. 465), which would scarcelyhave been supposed to belong to the same specific type did they notoccur upon the same stipe. The careful study of these varieties inevery instance in which any disposition to variation shows itself,so as to reduce the enormous number of species with which our sys-tematic treatises are loaded, is a pursuit of far greater real valuethan the multiplication of species by the detection of such minutedifferences as may be presented by forms discovered in newlyexplored localities; such differences as have already been pointedout being, probably, in a large proportion of cases, the result of themultiplication of some one form, which, under modifying influencesthat we do not yet understand, has departed from the ordinary more faithfully and
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