A history of Infusoria : including the Dismidiaceoe and Diatomaceoe, British and foreign / by Andrew Pritchard.
- Date:
- 1861
Licence: Public Domain Mark
Credit: A history of Infusoria : including the Dismidiaceoe and Diatomaceoe, British and foreign / by Andrew Pritchard. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![length^vise over its contiguous frastule ; tho second acts simultaneously in a similar manner with regai-d to the third, and so on throughout the whole filament,—the same action having been going on at the same time at both ends of the filament, but in opposite directions. The central frustule thus appeai-s to remain stationaiy, or nearly so,—while each of the others has moved with a rapidity iacreasing with its distance fi'om the centre, its own rate of movement having been increased by the addition of that of the inde- pendent movement of each fnistide between it and the central one. This lateral elongation of the filament continues until the point of contact between the contiguous fmstules is reduced to a very small portion of their length, when the filament is again contracted by the frustules sUdiug back again as it were over each other; and this changed direction of movement proceeding, the filament is agaiu draAvn out until the frustules are agaia only slightly in contact. The direction of the movement is then again reversed, and con- tinues to alternate in opposite dii'ections, the time occupied in passing from the elongation in one direction to the opposite being generally about 45 seconds. If a filament while in motion be forcibly divided, the uninjured frustules of each portion continue to move as before, proving that the filament is a compound structui'e, notwithstanding that its frastules move in imison. When the filament is elongated to its utmost extent, it is extremely rigid, and requires some comparatively considerable force to bend it, the whole filament moving out of the way of any obstacle rather than bending or separating at the joints. A higher temperature increases the rapidity of the movement. To this account Prof. Smith appends these observations:— The motion here so accurately described is not essentially different from that noticeable in many of the free species of Diatomese, the pecuharity being that it is here exhibited in numerous united frustules; when observed in a band of one hundred or more frustules, the singular appearances assumed by the filament under the action of so many individuals moving at one time in apparent concert, and another in opposition, never fail to excite astonish- ment. Mr. Thwaites's account conveys the impression that the movements are always regular: but this is not the case; for Mr. Ealfs teUs us, by letter, that both Dr. Bailey and himself have convinced themselves that they are at many times irregular. Dr. Don kin, in his description of a new species of Badllaria he names B. cursoria (J. M. S. 1858, p. 27), has the following account of its singular move- ments :— When the filament is in a quiescent state, the frustules are all drawn up side by side, their extremities being all in a Hne, thus forming a group. When a filament previously at rest resumes its activity, the movement] is commenced by the second or inner fnistule at one end of the filament gliding forward along the contiguous sui-face of the first or outer frustule until their opposite extremities overlap each other. This is soon followed by a similar movement of the third, foui-th, and fifth, &c., aU moving fonvard in the same direction, and each frustule gliding along the surface of the one preceding it, until they have extended themselves into a lengthened filament or chain. In the course of two or thi-ee seconds after this has been accomplished, a retrograde movement, exactly of the same character, begins to take place, and continues until the filament has retraced its course, and stretched itself out in a direction exactly opposite to the position it had previously occupied. This phenomenon is repeated again and again; and in this manner the whole group is kept in a state of activity for an indefinite period of time; and aU the while, if no impediment produces irregularity, tho outer or terminal frustule, next to which tho movement commenced, vudntains a stationary and fived position.](https://iiif.wellcomecollection.org/image/b21910224_0071.jp2/full/800%2C/0/default.jpg)
