10 ZOOPHYTES. 
treating of these subjects, we shall dwell with some minuteness on 
the structure of coral animals—their habits and modes of growth and 
developement; and it will be our aim to give such simple explanations 
as will be intelligible to the general reader, although it may require 
the stating of some principles well known to those versed in science. 
The mind should be disabused of the idea that all polyps form 
coral. There are many species identical in general structure with 
coral animals by which no coral is secreted. Among these, are the 
Actiniz,—common on some parts of our own coasts,—many of which 
are richly coloured and occasionally measure several inches in diame- 
ter, as is well shown by the drawings of Mr. Drayton on the first five 
plates of the Atlas. Other species contain scattered granules of lime. 
Thus there is a gradual passage up to the coral-making species, whose 
secretions form a solid framework to the animal. 
Another simple fact should be here understood. On examining 
any piece of coral, the surface is found to be covered either with pro- 
minent cells, or concave depressions ; hundreds, perhaps, to a single 
branch. Each of these cells marks the position of a polyp, and 
counting them we may ascertain the number of flower-animals that 
together constructed the branch. But this compound structure is not 
universal. Some coral-polyps are single animals, each a separate 
individual like the soft Actinia; and this is apparent in the coral, for 
it presents but a single cell or depression. From the solitary polyp, 
there are all possible varieties among zoophytes, up to living masses, 
in which hundreds of thousands are congregated, all the progeny of 
a single germ. 
Coral is above called the framework of the polyp. It is not a col- 
lection of cells in which polyps may conceal themselves, though so 
stated till a recent date. On the contrary, the coral is generally con- 
cealed within the polyp or polyps, and is literally an internal frame- 
work, having many analogies to a skeleton. 
With these few introductory explanations, we may enter upon the 
subject before us—the Structure, Habits, Classification, and Descrip- 
tion of Zoophytes. 
