LECTURE XII. 
203 
anti shall begin with a genus of the smaller corals 
called Sertiilaria. The genus Sertularia is re- 
markable for its vegetable appearance, and is po- 
pularly considered as a kind of sea-moss. It is a 
genus which contains a vast number of species, 
some natives of our own coasts, and others exotic. 
Most of the species are, wlien dried, of a pale, se- 
mitransparent, yellowish-brown colour, and di- 
vided into very numerous ramifications. In the liv- 
ing or fresh state, the animal or Polype part may 
be observed to till the whole, both of the stem and 
branches, and to send forth a head, with several 
arms, from every individual termination of the 
numerous branches. The whole therefore may be 
considered as a very compound or branched po- 
lype, defended by an elastic, horny covering. In 
the dried zoophyte the animal part shrinks up 
and becomes obliterated ; the cortical part or case 
alone remaining. One of the most elegant spe- 
cies of Sertularia, and at the same time one of the 
most simple in its structure, is the S. pinnata or 
pinnated Sertularia, which is a native of our own 
coasts, and is found adhering to rocks, and often 
to oysters and other shell-fish : it seldom exceeds 
the height of about two inches , and its appear- 
