56 
THE GEOLOGIST. 
simple gelatinons substance, having power of expansion according to 
its wants, and being able to secrete lime from the ocean, and perhaps 
to transmute chemically other salts into lime, with which it built arotmd 
itself a stony skeleton, a home to hve in, and a defence from injury. 
In accordance with the thread-like growth of the polyp, we shall find 
these stony houses built up in most cases of tubes, through which the 
animal extended itself, the open end or summit forming its communi- 
cation with the outer world. 
These tubes are in most species crowned with a certain number of 
ridges, disposed like the rays of a star ; these took their shape from 
the slender fisliing arms of the polyp, and formed their protection. 
The summit of the tube is called the calice, or cup, and the ridges 
that radiate from its centre are known as septa. The beautiful pat- 
tern that covers the surface of a coral is owing to the preservation of 
these star-like septa, and by the variation in their forms and number 
combined with altered shape of the calice we distinguish species. 
For in this tiny cup are printed more definitely than elsewhere the 
characteristics of its inhabitant. 
It is well to examine every piece of milleporal coral in three several 
ways. First, look at its upper surface and note the form and con- 
straction of its calices and the number, if any, of their septa ; then, 
turning it sideways, observe whether the tubes of which these calices 
are the termination are continued to the base of the coral, or die 
away in its substance, and lastly, look at the under-surface, notice if 
the basal plate is free axia unattached, or is furnished with a pe- 
duncle, or foot of attachment. But in describing the species, it is 
best to begin with the cup-corals. The normal form of this first 
great division of zoophytic life is that of a simple cup, produced by a 
polyp which expends all its strength in the development of a single 
cahce. In some species, however, such solitary polyps are aggregated 
together, sometimes accidentally so, as in CyatJwphyllum articulatwrn, 
usually found in groups of strongly -walled corallites, growing up to- 
gether without interfering with each other; and. in several species of 
cup-coral a peculiar method of reproduction— no less than " the life of 
the parent being continued m. that of the offspring," by buds grow- 
ing out of the centre of its calice, gives a composite character to what 
was before a solitary polyp. For the buds growing up and expand- 
