1903 



British Field Zoology 



251 



floating particles ; but its instincts are sometimes at fault. I have 

 amused myself often by putting small quantities of carmine or Prussian 

 blue into the water. The Vorticella swallows the 

 particles, so that its interior shortly presents brilliant 

 bits of colour in neatly rounded pellets ! This experi- 

 ment demonstrates the existence of a short oeso- 

 phagus, visible during the act of swallowing. 



Cilia — the lashing hairs just described — play an 

 important part in the animal world. Not only do 

 they serve to create currents in the water, as in 

 the case of a fixed Infusorian like Vorticella, but in 

 the free Infusoria they propel the whole organism 

 through the water. Again, in a very large number 

 of the higher animals the young or larvae are ciliated, 

 and propel themselves through the water in this 

 manner. The gills of molluscs and tadpoles are 

 covered with cilia, and so are many of the internal 

 surfaces (epithelium) of our own bodies. The cause 

 of the motion in cilia is mysterious. Unlike mus- 

 cular movements, it is certainly not nervous, since it 

 is seen in animals with no nervous system, whilst in 

 higher forms it goes on for hours after a piece of 

 the ciliated surface has been severed, or even after the death of the body. 

 We can only surmise that it is in some way connected with that diffused 

 sensibility which we attributed to the living protoplasm of Atnceba and 

 other Protozoa. 



One of the most striking characteristics of cilia is the ease with which 

 they can be formed or obliterated. They are indeed merely prolongations 

 of the cell-wall and the internal protoplasm. This is well shown during 



Fig. 9. 



a, Nucleus. 

 b, c, Mouth. 



$ 



(b 



=**/i\r 



J 



Fig. 10. 



J 



a, A single Vorticella. b, Withdraws and obliterates wreath of cilia. 



c, d, e, Divides into two halves. 



y, Cilia appear on one half, at first short and only waving slowly. 



g. The cilia increase in length and rapidity of movement and cause the bell to begin to 

 rotate till (//) it breaks away. 

 ! be half that remains attached to the old stem re-forms a ciliary wreath at its free end, 

 whilst the free-swimming bell attaches itself by its ciliated end, obliterates the cilia, 

 grows a stem, and forms another ciliary wreath at the opposite end. 



the process of self-division in Vorticella. I have watched this in the 

 microscope many a time, yet the sight never fails to rouse feelings of 

 wonder at the celerity with which the whole series of changes is accom- 

 plished. Under favourable conditions twenty to thirty minutes suffices. 



