30 SWIMMING AND CREEPING l'K( )T01'LASTS. 



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 cai-eful 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 othei-s, 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, perceptilily attracting it and deter- 

 mining the direction of its motion. It is very curious to watch the tiny pear- 

 shaped whirling protoplasts of Drcqxirnaldia, Ulothrix, 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^); oi-, 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 9.io. ") 

 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- 

 plasmic bodies during the rotatory and progressive motion caused by their cilia; 

 and the granules and chlorophyll-corpuscles dotted aliout in the bod}' 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 jjulsations, 

 l)ecause they are accomplished rhythmically and manifest themselves as alternate 

 expansions and contractions of the vacant space. 



In each of the motile protoplasts of ulothrix (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 Dra^ia'tmaldia two such vacuoles 

 may be observed close together, whose rhythmic action is alternate, so that the 



