The Swimming of Monas stigmatica Pringsheim and Peranema trichophorum (Ehrbg.) Stein. and Volvox sp. Additional Experiments on the Working of a Flagellum.

Summary.1 If the waves or impulses started at the tip of the flagellum in a mono‐flagellate organism, and travelled towards the base, the flagellum would obviously be held out in an extended position and draw the cell after it. This is the old and mistaken concept of the tractellum as described by Gray. It appears to be the result of deduction rather than observation or experiment, though surely the waves are more likely to start at the base of a flagellum than at the tip. 2 It has been proved, largely by means of high‐speed photomicrography, that the waves do start at the base of the flagellum, and not at the tip, in all organisms so far investigated, and hence the whole mechanical concept of the system requires drastic alteration. 3 In 1925 Krijgsman examined the movement of the longer flagellum of Monas by means of dark‐ground illumination. He clearly recognized that the waves started at the base of the flagellum; but since in his observations the organisms were placed in a compressor or were mounted in a drop of fluid between slide and cover‐slip, their movements were restricted and they were able to swim at only about one‐tenth of their normal speed. 4 The majority of the Monadaceæ swim rapidly, and one species, Monas stigmatica Pringsheim, covers a distance of forty times its own length in a second. 5 Krijgsman's paper constituted at the time a valuable contribution to our knowledge of flagellar movement, but it gives a totally wrong conception of the movements of the free‐swimming organism. 6 In flagellate organisms which swim forward rapidly, or cover several times their own length per second, e. g. Monas stigmatica or Polytoma uvella , the flagellum, or flagella, in which the waves start at the base, cannot be held in the extended position during normal swimming. They must be reflexed or bent backwards, and their function is to cause the organism both to rotate and gyrate. It is this rotation and gyration which provides the forward component. 7 In very slow‐swimming flagellate organisms, however, and especially in the colonial flagellates such as Volvox sp., the flagella are held out in the extended position and may precede the organism. The mechanics of the flagellar movement in this type of flagellum has been investigated experimentally and described. 8 The well‐known flagellate organism Peranema also moves forward very slowly, with the greater part of its single flagellum extended, but even so the tip of the flagellum is reflexed. However, it is doubtful whether the flagellum has any locomotory function in the normal movement of this organism. 9 The waves start at the base of the flagellum and not at the tip (Lowndes, 1936). 10 When stimulated by the shaking of the slide or by an electric shock, etc., the whole of the flagellum of Peranema is thrown into a succession of waves, but under these conditions the organism stops moving forward. It changes its direction and then proceeds as before. 11 These observations are in complete agreement with those of Verworn. 12 It is usually stated in text‐books, e. g. Gray (1928) and Borradaile and Potts (1941), that Peranema swims slowly forward when the waves in the flagellum are confined to the tip, but that it swims rapidly forward when the waves occur throughout the whole length of the flagellum. Verworn is usually held responsible for this statement, though he actually stated nothing of the kind. His observations were correct, while their more recent interpretation has been shown to be incorrect. 13 One of Krijgsman's diagrammatic figures has been reproduced by itself in more or less advanced British text‐books, and hence it is finding its way into the elementary text‐books. The figure in question is shown in fig. 1 B. It was originally given as a simplification of two other figures, and in conjunction with these and with its proper context it was perfectly sound, but taken by itself, and away from the proper context, it constitutes what can only be described as a travesty of elementary mechanics.