ANATOMY AND PHYSIOLOGY OP THE POEAMINIPERA. 179 
soutliern world. Here these accumulating shells constitute 
masses of unknown extent and thickness^ almost unmixed with 
either inorganic materials or with other organisms. They are 
forming raw material for the construction^ in some remote 
future^j of beds of calcareous rock^ as closely allied varieties 
did countless ages ago, when our chalk-hills existed in like 
manner as a calcareous mud at the bottom of the Cretaceous 
sea. But in all probability the bond of similar conditions 
is not the only link that unites the present with the past. 
We find many of the species referred to exhibiting no material 
variations, notwithstanding the widely different conditions 
under which they exist. In shallow waters or in the depths 
of the Atlantic ; in icy seas or under a tropical sun, they are 
ever the same. This indifference to external circumstances, 
arising out of then* low organization, has enabled them to 
survive changes fatal to all animals of higher organization; 
and it is more than probable that many of the existing 
Foraminifera are the lineal descendants of an ancestry that 
lived so far back as the Triassic period, a pedigree that sets 
at nought every attempt to vie with the antiquity of their 
pedigree. Other and more conspicuous creatures have again 
and again succumbed before the physical changes that suc- 
cessive ages have brought about; but these little objects 
pursue then wonted course, and bid fair to do so as long as 
the world endures. 
INDEX TO PLATE. 
1. Shell and soft animal of Miliola (after Scliiiltze). 
2. Shell and soft animal of Discorhma (after Schultze) with the foramina 
in the shell- wall. 
3. Shell and soft animal of Gromia (after Schultze). 
4. Lagena wilgaris. 
5. Nodosaria radicula. 
6. Dentalina legumen var. 
7. Cristellaria calcar var. 
8. Rotalma inflata. 
9. Spirillma perforata. 
10. Orbitolites, horizontal section (after Carpenter). 
11. Textularia variabilis. 
12. Miliolina trigonula, end view. 
13. Spiroloculina depressa var. 
14. Section of laminated shell-wall of an Operculina, showing the pseudopodian 
tubes penetrating the laminse. 
15. Section of shell-wall of an Amphistegina, sho^vhig the parietal canals. 
16. Parent hliliolina developing young germs (after Schultze). 
