GENUS ORBITOLITES GENERAL PLAN; COMPLEX TYPE 
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27. The disks of this complex type are not distinguished from those of the simple 
type already described, by any difference in the structure of the Nucleus ; and there 
is frequently nothing- specially characteristic in the structure of the zones that imme- 
diately surround it. Each of the peripheral zones, however, consists of two super- 
Jicial layers, an upper and a lower, and of an intermediate stratum ; — these will now 
be described seriatim. 
28. The superficial layers are formed of the (usually) oblong cells, whose contour 
is indicated by the surface-markings; when they are laid open horizontally, by rub- 
bing away the thin shell which covers them in (Plate VI. fig. 3), it is seen that the 
floor of each cell has an aperture at either end; but no communication can be 
traced, either through the side-walls between the contiguous cells of the same zone, 
or through the end-walls, between the cells of successive zones. Moreover, there is 
no such alternating arrangement of the cells of successive zones, as we have seen to 
prevail in the simpler type (^ 17); and they altogether seem to be quite independent 
one of another. When this superficial layer is examined in a vertical section having 
a radial direction (Plate VI. fig. 7)5 it is seen that the floors of its cells (a, a) are 
formed by the expanded summits id, d', d”) of the irregular septa, which separate 
from each other the columnar cells of the intermediate stratum (cccc); and that 
the apertures at the two ends of the floor are the entrances to passages (e, e', e"), 
which lead obliquely downwards (the passages on either side of the partition between 
two successive cells of the superficial layer inclining towards each other) towards 
these cavities. It is observable, moreover, that just at the point at which the con- 
tiguous passages meet each other, there is always a round aperture in the 
partition {g,g) which divides the contiguous cells of each zone ; and when, in a hori- 
zontal section, the superficial cells have been entirely ground away, so as to lay open 
the most superficial part of the intermediate stratum, this part is found to be traversed 
in each zone by a continuous circular canal (Plate VIII. fig. 3), with large rounded 
openings that lead into the columnar cells beneath. The meaning of this arrange- 
ment becomes obvious, when we examine the disposition of the animal substance 
which occupies these cavities ; for we find, as might have been anticipated, that the 
superficial cells are filled with segments of sarcode of corresponding shape (Plate IV. 
figs. 4, 7} aa) ; and that whilst these have no direct connexion with one another, 
each of them is connected by means of fleshy peduncles with the annular stolons 
bb that run along its extremities; whilst from the underside of these annular stolons 
(fig. 4) descend the thick columns of sarcode (cc, c'c'), which occupy the columnar 
cells of the intermediate stratum. The absence of any essential dependence of the 
segments of the superficial, and of those of the intermediate strata upon each other, 
seems indicated by the fact that there is no constant numerical relation between 
them, — a circumstance which extremely perplexed me, until I had ascertained, by 
examination of the animal, that the passages (Plate VI. fig. 7? e, e', e") debouch, not 
(as I had at first supposed) into the columnar cavities, but into the annular canal, 
