198 
DR. CARPENTER’S RESEARCHES ON THE FORAMINIFERA. 
to fifteen concentric zones. The arrangement and connexions of these zones may 
be made out in the thinnest and most translucent specimens, by examining them 
by transmitted light, after mounting them in Canada balsam ; this, however, gives 
such transparence to the thin shelly layer which is continuous over both surfaces, 
that it may escape notice (if not carefully looked for), so as to lead to the conclu- 
sion that the cells are open. Most specimens require to be somewhat reduced in 
thickness, by slightly grinding down one surface, to enable the arrangement of their 
interior to be distinctly made out; and this may be examined either by transmitted 
or by reflected light. Each zone thus seen in horizontal section (Plate V. fig. 1, c, c), 
consists of a circular set of small ovate cells, excavated, as it were, in the shelly sub- 
stance of the disk, and communicating with each other laterally by passages which 
unite them together into a continuous annulus. The zone which immediately sur- 
rounds the nucleus is connected with it by passages which extend from the outer 
margin of the large circumambient segment to the several cells of which it is itself 
composed ; and each zone communicates with the one on its exterior by similar 
passages, which usually extend, however, not from the cells of the inner zone to those 
of the outer, but from the connecting passages of the inner zone to the cells of the 
outer (Plate IV. figs. 8, 9) ; and thus it comes to pass, that the cells of each zone 
usually alternate with those of the zones that are internal and external to it. A ver- 
tical section of the disk, such as is shown in Plate V. figs. 4, 5, exhibits the same 
arrangement under a different aspect. The cells of the concentric zones are seen to 
be much higher than they are broad, so that they present a somewhat columnar 
form ; the proportion of their height to their breadth, however, may vary greatly in 
different parts of the same disk, the former often increasing from the centre towards 
the periphery (fig. 4), whilst the latter remains constant, or nearly so ; and the 
columns, instead of being straight, are generally more or less curved, and are some- 
times bent in the middle at an obtuse angle (Plate V. fig. 7? i)- The gradation 
which presents itself from one of these forms to the other, and their coexistence even 
in the same specimens, clearly proves that no value can be attached to the form and 
proportions of the cells, thus seen in a vertical section, as furnishing specific charac- 
ters. In every perfect specimen, the columnar cells are seen to be closed at their 
two extremities by a thin shelly wall; and this is sometimes flat, sometimes more or 
less convex *. — The meaning of these arrangements is clearly seen, when we turn our 
attention to the structure of the animal (Plate IV. fig. 1). For the outer margin of 
* In a large proportion of the specimens obtained from sands or dredging, the cells have been laid open by 
attrition ; either throughout the surface of the disk, if it should be flat, or at its margin only, if it should be 
at all saucer-shaped. The constancy of this last character in a certain set of forms, resembling that repre- 
sented in Plate VII, figs. 8, 10, might at first sight lead to the idea that they constitute a distinct specific type; 
but, as will hereafter appear, these plate-shaped disks cannot be separated by any definite line of demarcation 
from such as are quite plane ; and in specimens of them which have not suffered attrition, the marginal cells 
ate closed, like all the rest. 
