30 SWIMMING AND CREEPING PROTOPLASTS. 
As was mentioned in the description of Vaucheria the locomotion of ciliated 
protoplasts lasts for a comparatively brief period. It gives the impression of 
being a journey with a purpose: a search, as it were, for favourable spots for settle- 
ment and further development; or else a hunt after other protoplasts moving 
about in the same liquid. Green protoplasts always begin by seeking the light, 
but after a time they swim back into the shadier depths. Many of these, especially 
the larger ones, avoid coming into collision, and are careful to give each other 
a wide berth. If numbers are crowded together in a confined space, and two 
collide or their cilia come into contact, the motion ceases for an instant, but in a 
few seconds they free themselves and retire in opposite directions. 
Contrasting with these unsociable protoplasts are others, which have a ten- 
dency to seek each other out and to unite; and protoplasm acts in many cases 
on protoplasm of identical or similar quality, perceptibly attracting it and deter- 
mining the direction of its motion. It is very curious to watch the tiny pear- 
shaped whirling protoplasts of Draparnaldia, Ulothriz, Botrydium, and many 
others, as they steer towards one another and, upon their ciliated ends coming 
into contact, turn over and lay themselves side by side (fig. 7°); or, to see one 
pursued and seized by another, the foreparts of their bodies brought into lateral 
contact, and, finally, the two, after swimming about paired for a few minutes, 
fusing together into a single oval or spherical protoplast (fig. 7°). Even the 
minute fusiform protoplasts which are moved by cilia proceeding from the sides 
of their bodies (fig. 7°), as well as the spirally-coiled forms (figs. 7%™) 
endeavour to unite with some other protoplast. They always move towards 
larger protoplasmic bodies at rest, cling to them closely, and at last coalesce with 
them into single masses (fig. 7°). 
As a rule no striking change is to be perceived in the inside of motile proto- 
plasmie bodies during the rotatory and progressive motion caused by their cilia; 
and the granules and chlorophyll-corpuscles dotted about in the body of the 
protoplast seem to remain, throughout the period of locomotion, almost unchanged 
as regards both position and shape. It is only in the vicinity of certain little 
spaces, called “vacuoles,” in the substance of the protoplasm, that changes in 
many instances are observed, which indicate that, during the motion of the whole 
apparently rigid mass, slight displacements may also occur in the interior, some- 
what in the same way as, when a man walks, the heart inside his body is not still 
(relatively to the body), but continues to pulsate and cause the blood to circulate. 
The changes observed in vacuoles have, moreover, been described as pulsations, 
because they are accomplished rhythmically and manifest themselves as alternate 
expansions and contractions of the vacant space. 
In each of the motile protoplasts of Ulothria (fig. 8) there is found, near the 
conical end, which is furnished with four cilia, a vacuole which contracts in from 
12 to 15 seconds, and dilates again in the succeeding 12 or 15 seconds. In the 
swarm-spores of Chlamydomonas and those of Draparnaldia two such vacuoles 
may be observed close together, whose rhythmic action is alternate, so that the 
