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POPULAR SCIENCE REVIEW. 
narrow necks. It is to variations in the directions which 
these shoots assame that is due the diversified aspect of the 
Foraminiferous shells. In some the segments grow in a linear 
series_, each new one being projected in a straight line, as in 
Nodosaria (fig. 5), or in a curved one, as in Dentalina (fig. 6). 
In Marginulina and Cristellaria (fig. 7) the growth is first 
spiral, then straight. In another group all the growths 
commence and continue in the spiral direction. The simplest 
of these is the Spirillina (fig. 9), where the creature merely 
extends itself in a spnal coil without any transverse con- 
strictions, and, consequently, without any separation of its 
shell into chambers, after the pattern of the recent fresh-water 
genus of Mollusks, the Planorbis. But the spiral type is 
usually divided into segments. Occasionally the exterior of 
the shell is so smooth that the boundaries of the segments 
are only marked by white or translucent lines. But these 
boundaries are more frequently indicated by deep constrictions, 
especially when the shell is immature, giving the creature a 
lobate aspect. This latter form especially prevails amongst 
the Botalinse (fig. 8) and Nonioninse. In another group 
(Textillarige, fig. II) the new segments are added in two parallel 
longitudinal series, alternating to the right and left of a central 
line, whilst in the genus Yerneueilina there are three such 
series. The tropical seas furnish another type, not now found 
in our colder regions, though in the earlier Tertiary period 
they were as common here as they now are among* the Coral 
Islands of the- sunny south. This is the Orbitolites (fig. 10), 
in which, after a brief spiral growth, the new segments shoot 
out in one or more horizontal planes from all the circumference 
of the original germ, forming a beautiful circular disk, resembling, 
in their external aspect, the engine-turned back of a watch. 
This elegant form, common in the Tertiary sands of the Paris 
basin, was long regarded as a minute coral. 
From these symmetrical forms we pass to another less 
regular group, conducting us by gradations to the unsym- 
metrical skeletons of the sponges. In the curious Tinoporus, 
the early spiral arrangement of the chambers is soon exchanged 
for a less regular clustering of new segments on all sides of 
the primary ones, but with some faint retention of a concentric 
arrangement ; whilst in the Carpenteria we have not only 
a very irregular grouping of the segments, but the cavities 
of the latter are occupied by a spongiform body, containing 
silicious spicules, like those of some sponges. It is possible 
that these latter objects may be mere parasites ; but if they 
are part of the Foraminiferous organism, which high autho- 
rities believe them to be, these animals supply a very remark- 
able link uniting the Sponges and Foraminifera. Under all 
