THE MECHANISM OF LIFE 509 



the centre of motion in the same sense as the centres of the cen- 

 tral nervous system in higher animals are regarded. We can 

 present the result of these best by means of a vivisection-experi- 

 ment upon Lacrymaria. 



Lacrymaria olor belongs to the holotrichous Giliata and is dis- 

 tinguished by its very characteristic movements ; from these it 

 proves to be an exceptionally favourable object for experiment upon 

 the influence of the nucleus upon movement. In the condition of 

 moderate contraction it is flask-shaped and presents a trunk, neck, 

 and head (Fig. 252, a and V). When undisturbed, it is in restless 

 motion, every portion of the cell-body taking part in its peculiar 

 activity. The trunk undergoes constant changes of form of a peri- 

 staltic character. At times the neck extends into an extremely 

 long and slender thread, the anterior end of which lengthens, 

 shortens, bends about and gropes here and there between the par- 

 ticles of mud (Fig. 252, a\ and at times it suddenly draws together 

 like a stretched rubber cord, soon to begin its play anew. The 

 head, provided with long oral cilia, gropes about in all directions 

 upon objects in the water, the cilia seeming to run over them like 

 little feet. In this way the whole protist twitches constantly for- 

 ward and backward by the alternate direction of the strokes of the 

 cilia, so that it moves very little from one place and is engaged 

 chiefly in searching about with its long neck and head with rest- 

 less eagerness. If it be stimulated, it suddenly contracts and 

 swims in the condition of moderate contraction some distance back- 

 ward, then takes a forward direction and whirls forward through 

 the water at a furious rate, constantly turning about its axis. 



The macro-nucleus with the closely applied micro-nucleus lies 

 in the middle section of the trunk. 



It is possible with some patience to separate, under the micro- 

 scope, by sharp cuts the individual parts of the body, in which the 

 head, the neck, and the posterior end-piece of the trunk are always 

 non-nucleated, while the trunk itself contains the two kinds of 

 nuclei. The result of the cross-section is that in every piece the 

 ciliary motion is very much accelerated. All the pieces whirl 

 about their axis and through the water with furious rapidity in 

 the contracted condition. The enormous augmentation of ciliary 

 activity gradually passes away, and then every piece behaves 

 exactly as it behaved when in connection with the whole organism. 

 The nucleated trunk continues its metabolic movements, twitching 

 now forward, now backward, by changing the direction of the 

 ciliary stroke ; the neck at times stretches far out (Fig. 252, d) and 

 gropes restlessly about, although it possesses neither head nor 

 trunk, and at times contracts like a rubber cord (Fig. 252, c) ; 

 the head, being now free from the trunk, runs about 

 over the particles of mud in the water like an independent 

 individual by means of exactly the same ciliary motions as in the 



