History of infusoria, including the desmidiaceae and diatomaceae, British and foreign / by Andrew Pritchard.

  • Andrew Pritchard
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: History of infusoria, including the desmidiaceae and diatomaceae, British and foreign / by Andrew Pritchard. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    32/1074 (page 12)
    evident; but the cells continue linked together, and a filament is formed,which elongates more and more rapidly as the joints increase in number. This contiaued multiphcation by division has its limits ; the segments gradually enlarge whilst they divide, and at length the plant ceases to grow; the division of the cells is no longer repeated; the internal matter changes its appearance, increases in density and acquires starch-granules, which soon become nume- rous • the reproductive granules are perfected, and the individual perishes. In a'filament the two oldest segments are found at its opposite extremities; for so long as the joints divide, they are necessarily separated further and further from each other. Whilst this process is in progi'ess, the filament in Sphcerozosma consists of segments of aH sizes (1.11); but after it has reached iMturity there is httle inequality between them, except m some of the last- formed segments, wHch are permanently smaUer. The case is the same with those o-enera in which the separation of the cells is complete.... It is obvious that the new portions must arise from the whole of the junction-margm ot the original valves; consequently when the junction occupies only a part ot the breadth, the new portion will be narrower than the old; but when the iunction of the valves is as broad as the ceH, the new portion [wtU from the beginning be of the same breadth, and wiU remain undistinguishable by its size when fission is complete. „ . ,, ^ a Mr. Balfs goes on to say that, when the ceU is oblong or only rounded at the extremities, the process, though similar, is less evident; the ceU at first seems merely to elongate (II. 11), ^y^^^^'^^'^'^^l^^'J^ oinal length, when the division commences, and the rounding of the new ends Smes apparent. The tapering cells present but little difference, for the sepTation tekes place before the extremities are fiilly developed; sometames these cells separate obhquely, as m Spirotcmia:' The mode of seK-division in Closterium has been illustrated by the ]^v. Mr Osborne (J. M. S. 1854, p. 57), from whose account we abstract the toi- S particulars:- I have (he says) watched for hours the proce^ of complete self-division; one-haK of the frond has remained pas^ve the othei haXd a motion from side to side, as if moving on an axis at the Point °f iiSctoe ; the separation has become more and more ^rdenVte motaon more aST-ntU at last, with a jerk, one segment leaves the otheiV' each tog one eitremity-the one newly formed along the hue of junction of the two segmen s-Juch more obtuse than the other. The circidation of the con- 5m globules for some hours previous to subdivision, and for some few hours afterwards, runs quite round the obtuse end of ^l^e endochi-ome Previously to complete separation each segment begins to show a central constriction of its endochrome, wHch in due time extends across the new frond, and constitutes the median clear space or band. ,,„„7;„„ A true reproductive act is presented by the act of conjugahon, or couphi^ of two fronds, and by the resultant development of a «P°?-^^^^j,?^^^; ^' XVI 11 12,13,14): This process consists in the apposition and subsequent ^tercommuMcation of the cavities and contents of bvo cells, -^y /;^. free, or othei-wise, members of a chain or filament. It is an act to the Desmidiea. but common to them along with the DiatomeaB and Con Latl In the family Conjugate (says Mr. Ralfs) the cells /'^'^•l^f^f StstiU forming parts of a filament; but in the Desmidie^e the filamcnt^^^^^ ledes almost invariably separate into single joints before therr cowboy and in most of the species the valves of the cells become detached after they a?e cmp^cd of their contents. To bring about the necessary apposition it fs usil for the conjugating cells to expand or bulge out on those sides which nreTcome into uidon; and whilst this is proceeding, the vesicles or globules