232 



LIFE, IX ITS INTERMEDIATE FORMS, 



however, as this motion is, so that it is impossible to look 

 at it without admiration, it is not really a progression of 

 any of the parts. This appearance of moving teeth is 

 caused by very fine cilia, the nature and action of which 

 have already been explained It will be sufficient here to 

 say, that the combined action of the whole of the cilia 

 forms a whirlpool, the centre of which is the mouth at the 

 bottom of the bell of tentacles, and that every atom that 

 comes within range is sucked in and engulphed. 



This is a representative of a class of animals called 

 Polyzoa ; it contains numerous genera and species differ- 

 ing much in the form and arrangement of the cells, but 

 displaying a remarkable uniformity in the structure of the 

 animals themselves. In many species the series of cells 

 is attached to a foreign body only 

 by its base, standing erect, often 

 spread out and divided like a 

 much-cut leaf, or set in single 

 order, one cell springing out of the 

 tip of another, and bearing a third 

 on its extremity, with occasional 

 branchings, so that the total 

 structure resembles a tiny shrub. 



Many of these creatures bear 

 highly curious appendages, than 

 which we know scarcely anything 

 Buguiaavicuiaria(naf.«*),and more interesting as a microsco- 



a cell magnified, shewing the _r 



expanded poiypide, and a pical study. Take, for example, 

 "bird's-head." Bicellaria ciliata, or Bugula avicu- 



laria. On the outside of some of the cells in these species 

 there is a little tubercle, to which is articulated, by a 



