206 
LECTURE Xtl. 
Tubularia. The marine genus called Flustra at 
first view so much resembles 2ifucus or sea- weed, 
that it has been commonly described as such be- 
fore the time of Mr. Ellis, who determined its 
real nature. It consists of flat, branched, leaf-like 
processesj each composed of very numerous cells, 
of a slightly horny or tough substance, open at the 
top, and aflbrding a passage to the animal part or 
polype-head, which, in the recent zoophyte, pro- 
trudes through each cell j and the regular manner 
in which the cells are disposed, gives the leaf or 
plant-like appearance to the whole. The most 
common species is the FI. foliacea, or broad-leaved 
Flustra, common on our own coasts. 
I shall now proceed to give an example or two 
of the principal genera of the hard or strong 
Zoophytes, more generally^ called Corals. Of these 
some are furnished with a kind of horny stem or 
central part, covered over throughout all the rami- 
fications by a soft bark of a calcarious nature, and 
in which the animal or polype-like fabric is placed, 
while in other species the central part or stem is 
of a stony hardness, and is covered, in a similar 
manner, by a softer bark containing the animal 
part. The most remarkable genus of the hard 
