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, 



Fig. 8.— Pulsating Vacuoles iu 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 



