446 



NATURE AND MAN. 



time on the coast of Australia, the Fiji reefs, and other Pacific 

 shores, and found fossil in the early Tertiary limestones of the 

 north of France, one bed of which is in great degree formed of 

 an accumulation of disks very similar to those now piling them- 

 selves up near its Antipodes. 1 was supplied, moreover, with 

 a series of smaller disks (chiefly picked out of shore-sands), down 

 to an almost microscopic minuteness, but agreeing with the larger 

 in this fundamental feature of their structure, — the arrangement 



Fig. I. 



Shelly Disk of Orbltolifes complanata, showing concentric rings of 

 chamberlets, arranged round a central nucleus. 



of their mutually connected " chamberlets " in successive circles 

 round a central "nucleus," their plan of growth being thus ry^r/zW. 

 This plan is most fully carried out in typical specimens of the 

 large Orbitolites complanata (Fig. I.) ; in which the " sarcodic 

 nucleus," consisting of a flask-shaped " primordial segment," a, 

 Fig. IL, and of a "circumambient segment," b, b\ c, is at once 

 surrounded by a complete ring of sub-segments, separately budded 



