DR. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 
557 
the former, whilst in the multiplication of its nuclei it obviously tends towards the 
latter. 
The growth of this beautiful organism doubtless takes place after the completion of 
the first annulus, in the manner described in my former Memoir (§ 35). The sarcodic 
body, when enlarged by the nutriment it has appropriated, will project itself through 
the marginal pores, in quantity sufficient to form, by the coalescence of its separate 
protrusions, a continuous belt of sarcode; and in the substance of this a set of 
radial calcareous partitions will be deposited, commencing between the pores of the 
margin of the previous shell-ring, while two horizontal lamellae are formed on the 
superficial planes, to constitute, as it were, the floor and ceiling of the new circle of 
chamber]ets. These horizontal lamellae overlap but very slightly the margin of the 
previous annulus (Plate 37, fig. 3, a, a) ; and their adhesion to it is generally so weak 
that the annuli readily come apart. As the subdivision of the annulus into 
chamberlets does not extend to its outer portion, a passage is left (seen in vertical 
section at b, b, b, fig. 3), which is occupied by a continuous ring of sarcode, as shown in 
Plate 38, fig. 1 ; and from this ring proceed the stolons which pass outwards through 
the pores of the septum that closes it in. 
The homogeneousness of the protoplasmic substance by which the entire cavitary 
system is occupied, is shown (as in the types formerly described) by the completeness 
with which the effects of injuries are repaired, and the plan of the original fabric 
restored (see Phil. Trans., 1856, Plate VIII., figs. 4-9). Not only is the loss of any 
part of the disk repaired by the formation of a new and continuous annulus along the 
broken as well as the unbroken margin, so that the next and all succeeding zones 
follow the new contour (as shown in Plate 37, fig. 6) ; but a new and entire annulus 
of chamberlets may form itself around the whole circumference of a mere marginal 
fragment (fig. 7), by the enclosure of which in a subsequent succession of annuli, the 
discoidal form characteristic of the type is completely and characteristically restored. 
Owing to the transparence of these attenuated disks, I have been able to assure 
myself that every part of the margin of this fragment, whether broken or unbroken, 
peripheral, central, or lateral, has contributed to the formation of the first new 
complete annulus, by which the foundation was laid of the subsequent regular series 
of concentric zones; thus clearly indicating that a sarcodic extension took place from 
every chamberlet laid open by the fracture, as well as from the normal pores of the 
last-formed septal plane, and that these extensions coalesced to form a continuous ring, 
as in the formation of the ordinary succession of concentric annuli. 
This perfect reproduction of a form of peculiar regularity, in a type of animal organisa¬ 
tion so low that its body-substance does not show any advance upon the primitive proto¬ 
plasmic condition, is, in itself, a matter of great interest. But the interest is much 
enhanced by the consideration that this organism begins life, and forms its first shelly 
envelope, upon a plan altogether different; exchanging this for its later mode of 
growth, by a transition so rapid as to manifest the almost sudden attainment of a 
MDCCCLXXXItl. 4 c 
