. The microscope and its revelations. eseries, alternating with each other on the two or more sides of arectilinear axis ; here, again, the forms of the individual chambers,and the mode in which they are set one upon another, vary in sucha manner as to give rise to very marked differences in the generalconfiguration of the shell, which are indicated by the name it —Returning once again to the simple monothala-mous condition, we have in Orbulina—a minute spherical shell thatpresents itself in greater or less abundance in deep-sea dredgings,from almost every region of the wo
. The microscope and its revelations. eseries, alternating with each other on the two or more sides of arectilinear axis ; here, again, the forms of the individual chambers,and the mode in which they are set one upon another, vary in sucha manner as to give rise to very marked differences in the generalconfiguration of the shell, which are indicated by the name it —Returning once again to the simple monothala-mous condition, we have in Orbulina—a minute spherical shell thatpresents itself in greater or less abundance in deep-sea dredgings,from almost every region of the world—a globular chamber withporous walls, but destitute of any general aperture, the office of whichis served by a series of larger pores scattered throughout the wall ofthe sphere. It has been maintained by some that Orbtdina is reallya detached generative segment of Globigerina, with which it isgenerally found associated. The shell of Globigerina consists of anassemblage of nearly spherical chambers (fig. 619), having coarsely. FIG. 619.—Globigerina biiUoi/lcs as seen in three positions. porous walls, and cohering externally into a more or less regularturbinoid spire, each turn of which consists of four chambers pro-gressively increasing in size. These chambers, whose total numberseldom exceeds sixteen, mav not communicate directlv with each • «/ other, but open separately into a common vestibule which occupiesthe centre of the under side of the spire. This type has attractedgreat attention, from the extraordinary abundance in which it occursat great depths over large areas of the ocean bottom. Thus its minuteshells have been found to constitute no less than 97 per cent, ofthe ooze brought up from depths of from to •_>.(»()() fathomsin the middle of the northern parts of the Atlantic Ocean. Theyounger shells, consisting of from eight to twelve chambers, arethin and smooth, but the older shells are thicker, their surface israised into ridges that form an
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
