. The microscope and its revelations. the convolutions are usually least on one side (fig. 17); but among the nautiloid tribes it morefrequently happens that the last-formed whorl encloses the preceding 798 MICROSCOPIC FORMS OF ANIMAL LIFE to such an extent that they are scarcely, or not at all. visibleexternally, as is the case in Cristellnria (fig. 17), Polystdmella (fig. 23),and Nonionina. The turbinoid spire may coil so rapidly round anelongated axis that the number of chambers in each turn is verysmall; thus in Glohiyerina (figs. 20, 21, Plate XIX) there areusually only four; a
. The microscope and its revelations. the convolutions are usually least on one side (fig. 17); but among the nautiloid tribes it morefrequently happens that the last-formed whorl encloses the preceding 798 MICROSCOPIC FORMS OF ANIMAL LIFE to such an extent that they are scarcely, or not at all. visibleexternally, as is the case in Cristellnria (fig. 17), Polystdmella (fig. 23),and Nonionina. The turbinoid spire may coil so rapidly round anelongated axis that the number of chambers in each turn is verysmall; thus in Glohiyerina (figs. 20, 21, Plate XIX) there areusually only four; and in Valvvlnia, the regular number is onlythree. Thus we are led to the SiseriaZ arrangement of the chambers,which is characteristic of the textnlarian group (fig. s, a, b, and .».Plate XVIII), in which we find the chambers arranged in two rows,each chamber communicating with that above and that below iton the opposite side, without any direct communication with thechamber of its own side, as will be understood by reference to fig. FIG. GOl.—DlsrorliiiHi i/fiili/ilnrix i ItoKitlii/tt i-ftrians, Schultze),with its pseiulopodia extended. »i±J. A. which shows a cast of the sarcode-body of the animal. (>nthe other hand, we find in the nautiloid spire a tendency to pass(by a curious transitional form to be presently described) into theci/clictf mode of growth ; in which the original segment, instead ofbudding forth on one side only, developes (ji/mi/n all round, so thaia riny of small chaml)ers (or ehamberlets) is formed around theprimordial chamber, and this in its turn surrounds itself after t lielike fashion with another ring; and by successive repetitions of thesame process the shell conies to have the form of a disc made up ofa great, number of concentric rings, as we see in Orbitolites (tig. )and in (i/rtl<in / <//-i»i-(// were made by ace I 18 11 • • . j| 0 , . <•
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
