. The microscope and its revelations. fter examinationof them under the binocular microscope, especially with the black -ground illumination. The form of the valves in most of the spec-it-sis circular or nearly so; some are nearly flat, whilst in others thetwist is greater than in the species here represented. Some of thespecies are marine, whilst others occur in fresh water; a verybeautiful form, the C. clypeus, exists in such abundance in theinfusorial stratum discovered by Ehrenberg at Soos, near Ezer. inBohemia, that the earth seems almost entirely composed of it. The next family, the /Str
. The microscope and its revelations. fter examinationof them under the binocular microscope, especially with the black -ground illumination. The form of the valves in most of the spec-it-sis circular or nearly so; some are nearly flat, whilst in others thetwist is greater than in the species here represented. Some of thespecies are marine, whilst others occur in fresh water; a verybeautiful form, the C. clypeus, exists in such abundance in theinfusorial stratum discovered by Ehrenberg at Soos, near Ezer. inBohemia, that the earth seems almost entirely composed of it. The next family, the /Striatellece, forms a very distinct group,differentiated from every other by having longitudinal costse on theconnecting portions of the frustules, these costse being formed bythe inward projection of annular siliceous plates (which do , reach to the centre), so as to form septa dividing the cavityof the cell into imperfectly separated chambers. In some instancesthese annular septa are only formed during the production of the. FKJ. 454.—Cainpi/lodisc-us costatus: A, front view; B, side view. valves in the act of division, and on each repetition of such produc-tion, being thus always definite in number ; whilst in other casesthe formation of the septa is continued after the production of thevalves, and is repeated an uncertain number of times before therecurrence of a new valve-production, so that the annuli are indcjin //2)the septa have several undulations and incurved ends, so as to formserpentine curves, the number of which seems to vary with thelength of the frustule. The lateral surfaces of the valves in very finely striated, and some species, as (/. subtilissimaand (T. »iarina, are used as test-objects. The frustules in most ofthe genera of this family separate into zigzag chains, as in Dtatoma;but in a few instances they cohere into a filament, and still morerarely they are furnished with a stipe. The small fa
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
