226 
THE VOYAGE OF H.M.S. CHALLENGER. 
To determine the minute structure with any degree of completeness, and especially 
the nature of the communication that subsists between the chamberlets, would require a 
number of sections made on different planes, and for these the necessary specimens 
are not at present forthcoming ; nevertheless, with the help of allied organisms, the 
anatomy of which is well known, the available material is sufficient for the elucidation of 
all the more important and characteristic features. 
A preliminary examination brings one fact into prominence, namely, the close analogy 
that exists between the arrangement of the chamberlets in the sectional view and that 
found in the genus Orbitolites ; indeed there is scarcely any portion of the section to 
which a counterpart may not be found amongst the figures which accompany Dr. 
Carpenter’s memoir on the latter type. 1 It must, of course, be borne in mind that the 
section of a spherical test does not, like the horizontal section of an Orbitolite, present a 
series of chamberlets grouped on a uniform level, the whole of which, together with their 
means of intercommunication, can be seen at one time, but represents rather the aspect 
of a plane projected through a mass of cells so arranged that they are necessarily 
intersected at different angles. 
It may be noticed that although the section (fig. c.) passes through nearly the centre 
of the shell, it does not show any distinct primordial chamber. It is probable, therefore, 
that the initial chamber is of small size and perhaps scarcely distinguishable from the 
chamberlets, as is often the case in Orbitolites of the simple type. The early layers are 
comparatively thin and the constituent chamberlets small ; and either for this reason or 
because the centre of the section happens to be thicker than the rest, the arrange- 
ment appears somewhat confused, and not without a certain resemblance to the 
labyrinthic structure of some of the complex Alveolince. 
Referring to fig. d., which represents part of the section near the periphery 
much more highly magnified, it will be seen that the communication between the 
successive layers is maintained by tubular orifices, 1, 1, 1, 1, one at the margin of each 
chamberlet, and that these orifices are set obliquely close to the line of union with the 
contiguous chamberlets. In the external layer they serve collectively as the general 
aperture of the test, and correspond to the marginal pores of the Orbitolite; but they 
are not so conspicuous on the exterior, owing to their peculiar position and oblique 
setting. The chamberlets of the successive layers are neither regularly alternating, as in 
the simple Orbitolite, nor directly superimposed ; and although there is a certain degree of 
uniformity in their relative positions, they are too variable in size and shape to conform 
to any rule in this particular. 
The communication between the chamberlets of the same layer is maintained by short 
lateral stoloniferous tubes, which are less easy to identify than those uniting the successive 
layers already described. They are shown, in section, in fig. d., 2, 2, 2, 2. Under 
1 Phil. Trans., 1856. 
