SWIMMING AND CREEPING PROTOPLASTS. 31 
systole (contraction) of the one always takes place synchronously with the diastole 
(expansion) of the other. The contraction often continues until the cavity entirely 
disappears. It must depend, as also does the expansion, on a displacement of that 
part of the protoplasm which immediately surrounds the vacuole. But such a 
motion as this in the protoplasmic substance, even if only visible in a small part 
of the whole body, can scarcely be without its effect on other more distant parts; 
and it may, therefore, be concluded that the interior of a protoplast, endowed with 
ciliary motion, rotatory and progressive, does not remain quite at rest relatively, 
as seems on cursory inspection to be the case. 
Protoplasts whose motion is effected by means of cilia have no more need of 
their vibratile organs when once they have reached their destination. The cilia, 
\y 
Fig. 8.—Pulsating Vacuoles in the Protoplasm of the large Swarm-spores of Ulothrix. 
whether numerous or solitary, whether short or long, first of all become stationary 
and then suddenly disappear. Either they are drawn in or else they deliquesce 
into the surrounding liquid. Whether the motile protoplasts have come to rest 
because they have reached a suitable place for further development, as happens 
in Vaucheria, or because they have united, like with like, into a single mass, 
the form taken by the resulting non-motile body is always spherical. The final 
act is the development around itself of an investing cell-membrane, so that its 
soft and slimy substance may be protected by a firm covering from external 
influences. 
Essentially different from the motion just described is that of certain proto- 
plasts which are unprovided with cilia, but perpetually change their outlines, 
thrusting out considerable portions of their gelatinous bodies in one direction or 
another, and at the same time drawing in other parts. At one moment they 
appear irregularly angular, shortly afterwards stellate; then, again, they elongate, 
become fusiform, and gradually almost round (fig. 9). The protruded parts 
are sometimes delicate, tapering off into mere threads; sometimes they are com- 
paratively thick, and have almost the appearance of arms and feet in relation 
to the principal mass. The motion is not in this case like boring, but is best 
described as creeping. As one or a pair of foot-like appendages is thrown out 
