56 



THE GEOLOGIST. 



simple gelatinous substance, having power of expansion according to 

 its wants, and being able to secrete lime from tbe ocean, and perhaps 

 to transmute cbemically otber salts into Hme, with whicli it built around 

 itself a stony skeleton, a bome to live in, and a defence from injury. 

 In accordance witb tbe tbread-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 fishing 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. 

 Eor 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. Pirst, look at its upper surface and note the form and con- 

 struction of its calices and the number, if any, of their septa ; then, 

 turning it sideways, observe whether the tubes of which these calices 

 sjce 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 and 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 nonnal 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 

 calice. In some species, however, such sohtary polyps are aggTegated 

 together, sometimes accidentally so, as in Gyatliophyllum articulatwrii, 

 usually found in groups of strongly- walled corallites, gTowing 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 in that of the ofispring," by buds gTow- 

 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- 



