10 GUIDE TO THE CORAL GALLERY. 



the rocks (chalks and limestones) of the earth's crust, and at the 

 present time are covering millions of square miles of the ocean floor 

 with a pinkish-white mud or ooze, formed chiefly of their skeletons. 

 The shells of GloUgerina hulloides (Fig. 7 ; and specimens and figures 

 in Introductory series), a species which lives at the surface of the 

 ocean, form a large proportion of the ooze, which is hence termed 

 " Globigerina Ooze." .The piece of dark-coloured Tertiary Nummu- 

 litic limestone (Fig. Gj exhibited in the Case, formed part of the 

 debris from the summit of a Himalayan peak 19,000 feet above the 

 sea-level. The occurrence of this ancient sea-floor in its present 

 position affords clear proof of the elevation of the peak within — 

 geologically speaking — comparatively recent times. 



The large plaster models of BllocuUna illustrate " dimorphism," 

 a phenomenon now found to be of frequent occurrence in Foramini- 

 fera, and attributed to alternation of generations. 



One of the vertical sections shows a large central chamber 

 (megalospheric form), and the other shows numerous small ones 

 (microspheric form). Parallel series of fossil Nummulites (see 

 Introductory series and Family X.) are often found together in a 

 stratum, disks with small central chambers occurring along with 

 usually smaller disks with large central chambers ; formerly the two 

 kinds were regarded as different species, but are now considered to be 

 different forms of one and the same species. 



Radiolaria. 



The characteristic feature of the Radiolaria is the presence of a 

 membranous " central capsule " dividing the body into two zones, an 

 intra-capsular zone including the nucleus, and an extra-capsular 

 whence the pseudopods radiate. The vast majority form a skeleton 

 of silex or of acanthin, a horny organic material ; a few species 

 are without a skeleton. 



The Radiolaria live in the warmer waters of the ocean, mostly at 

 or near the surface, but some species exist only in the deeper zones. 

 Over vast areas in the tropical Pacific and Indian Oceans, and at 

 depths of about 3,000 fathoms, the ocean floor is composed of an 

 ooze chiefly made up of the skeletons of Radiolaria, and hence 

 termed Radiolarian Ooze. Certain rocks, as, for instance, Barbados 

 Earth, are largely or almost entirely composed of Radiolarian 

 skeletons. 



AVheu floating alive at the surface, Radiolaria are often richly 



