232 
LIFF, IN ITS INTERMEDIATE FORMS. 
however, as this motion is, so that it is impossible to look 
at it without admiration, it is uot 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 avid divided like a 
much-cut leaf, or set in single 
order, one cell springing out of the 
tip of another, and bearing a third 
oil 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 
more interesting as a microsco- 
Take, for example, 
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 
Bugula avicularia (nat. aud 
a cell magnified, shewing the 
expanded polypide, and a piCfU Study, 
“bird’s-head.” 
