AUTONOMOUS LOCOMOTORY MOVEMENTS 533 



of the typical cell, i. e. protoplasm, nucleus as well as chloroplasts. They are 

 almost always elongated, ovoid or pear-shaped, always markedly polar, but by 

 no means always exhibiting radial structure in relation to their long axis. One 

 pole, the anterior one in any movement, is generally free from chlorophyll and 

 provided apically, or not infrequently laterally, with two, four, or more cilia. 

 The posterior end is generally more rounded and contains chloroplasts. The 

 movements are by no means simple, consisting as they do not only in a forward 

 movement in the direction of the long axis of the cell but also a torsion on it. 

 This is at least true in the case of certain cells ; in other instances the move- 

 ment is more comphcated still. The forward movement may, instead of being 

 in a straight line, be in the path of a long drawn out spiral, the body of the cell 

 rotating on its axis at the same time, the axis remaining parallel to that of the 

 spiral. Finally a third type of movement is met with, when the anterior end of 

 the swarmspore advances in a spiral manner while the posterior end maintains 

 a straight course. If there be no mechanical or stimulating interference to its 

 movements the swarmspore continues to follow the direction taken at the com- 

 mencement of its movement, which on the whole is approximately a straight line, 

 but in other cases the spores swim in curves or move about quite irregularly. 



When the swarmspore meets with a mechanical obstacle it is able without 

 moving from the spot to institute a twisting movement, frequently recoiling or 

 moving backwards, twisting on its axis in the opposite direction. The butt end 

 is anterior in this movement but very soon the original forward movement is 

 resumed. Apart from the backward movement, the torsional movement changes 

 only in certain free swimming cells ; in the majority of cases the direction of 

 torsion is constant and characteristic of the species. 



All these phenomena may be observed in swarmspores only if these 

 movements be retarded, and this is best effected by replacing the water- 

 culture by a weak solution of gum. The absolute rapidity of movement of 

 the swarmspores, which is markedly dependent on external conditions, is by 

 no means great. It appears to be considerable only when looked at under the 

 microscope, but then it must be remembered that the distances are also magnified. 

 According to Hofmeister (1867) the movements are most rapid in the swarm- 

 spores of Fuligo varians, viz. about i mm. per second ; the swarmspores of Ulva 

 attainaspeedof 0-15 mm. per second (Strasburger, 1878), but the antherozoids 

 of the fern move much more slowly — 0-015 to 0-030 mm. per second — accord- 

 ing to Pfeffer (1884). 



The fern antherozoids, which we shall study more in detail in the next 

 lecture, differ from the zoospores of Algae in their form only but not in their 

 movements. They consist of a spirally twisted body with 2-4 coiis (Fig. 107, 

 p. 359), tapering gradually from base to apex, the cilia being inserted on the 

 thinner anterior spirals. No alteration in the form of the cell takes place here 

 either during the movement. 



That the cilia are the agents concerned in the movement may be easily 

 proved. If a swarmspore be cut in two, only the part bearing the cilia remains 

 capable of movement. If, by mechanical means, the cilia be removed, all move- 

 ments cease and the body of the swarming cell sinks to the bottom. How the 

 cilia bring about the forward movement, and, at the same time, the torsion, has 

 not been investigated in detail, but we can scarcely be mistaken if we assume 

 that the lashing of the cilia are carried out in the same way as Verworn (1901) 

 has demonstrated in the case of the ciliate Infusoria (Fig. 166). The apex of 

 the cilium is seen at first to lie parallel with the forward path of the animal and, 

 in the left-hand diagram (Fig. 166), the successive positions taken by the cilium 

 at short intervals are figured ; the withdrawal (right-hand figure) is effected by 

 other curvatures which are much slower, otherwise a forward movement would 

 be impossible. The rotation of the body is due to the fact that the curving of the 



