In the illustration the Actinurus is shown in two attitudes. In the upper figure it is represented as having the fore-part of the body entirely, and the tail part nearly, withdrawn within the central portion. The lower figure shows the same specimen with all its telescopic tubes drawn out to full length.
The creature is perpetually elongating and contracting its body by means of these tubes, so that a measurement of its length is not easy to obtain.
A full and interesting description of this curious Rotifer may be found in Gosse’s “Evenings at the Microscope,” p. 300. The long tails of the Rat-tailed Maggot, already described under the head of Diving, are good examples of the drawtube as found in Nature.
Locomotion.—Direct Action.
The second point which has to be elucidated is that or progress by means of Direct Action.
We have already seen how vessels can be propelled by sail, oar, paddle, or screw. We have now to consider a mode of progress which requires none of these things, but which works by means of Direct Action.
Such, for example, is the progress of a Rocket through the air.
The heated gases rush out with tremendous violence, and, by their pressure, urge the heavy rocket into the air with the rush, roar, and bang so familiar to all who have witnessed a good display of fireworks.
A rocket in the act of ascent is shown in the uppermost figure of the accompanying illustration.