GENUS ORBITOLITES: — VARIATIONS IN SURFACE-MARKINGS. 
217 
is not a body of constant shape, provided with organs having a fixed relation one to 
another, but is a mass of almost homogeneous sarcode, which in the living state is 
continually undergoing changes of form, one part extending itself into pseudopodia, 
whilst another undergoes a corresponding contraction, a strong a priori improba- 
bility is seen to exist, that, in animals of such organization, the form of the compo- 
nent segments should possess that value as a specific character, which it can only 
derive from constancy. 
53. Besides those regular markings of the surface, which correspond to the divi- 
sion of the interior into cells, a peculiar aspect is frequently given to it by the 
deposit of calcareous thickenings, which are sometimes irregular, but which occa- 
sionally present an approach to symmetry. The most remarkable example I have 
met with, of this kind of addition, is delineated in Plate VII. fig. 11, in which it will 
be seen that the deposit has taken place in radial lines disposed with a certain 
degree of regularity. But in fig. 10, which represents a specimen whose surface is far 
less altered by these deposits, no such symmetry presents itself; and other specimens 
in my possession exhibit the means between these extremes. Hence we are justified 
in pronouncing this peculiarity to result from an accidental outgrowth, which is so 
variable in its degree as not to afford the least basis for specific differentiation. It 
is worthy of note, however, that it presents itself far more frequently, and also in a 
far more characteristic manner, in the Orbitolites of the Philippine Seas, than in 
those of the Australian or of any other provinces ; and this circumstance seems to 
render it probable, that the outgrowth is directly due to the influence of some exter- 
nal conditions, probably to an excess in the proportion of carbonate of lime in the 
waters inhabited by these particular specimens. 
54. Variations in Mode of Gro?c^A.— Although the cyclical mode of growth, when 
once established, is subsequently maintained with great regularity, and although in 
what may be considered the typical form, it commences from the ‘nucleus’ itself, 
yet there are numerous instances in which the typical regularity is more or less 
widely departed-from, so that the early increase seems to take place after an alto- 
gether different plan. The most marked antithesis to that regularly concentric type 
of growth, in which a complete annulus of cells is formed around the large circum- 
ambient segment of the ‘ nucleus ’ (see ^17, also Plate IV. fig. 5, and Plate VII. fig, 2), 
is presented by those forms in which this circumambient mass only gives origin to 
new cells at its extremity ; these in their turn bud-forth others, which extend and 
multiply themselves laterally as well as in advance ; and thus a kind of spiral is pro- 
duced, which opens-out very rapidly, the lateral portions of its mouth tending to 
grow-round and embrace the nucleus. Thus, starting from the central globular 
mass, 1, of Plate IX. fig. 4, we see that the circumambient mass 2 2, which nearly 
surrounds it, gives origin at one of its extremities to a smaller mass, 3, from which 
bud-off two cells, 4 4, which again give origin to four cells, constituting the row 5 5. 
The cells of the next row, 6 6, are more numerous, but are themselves exceeded by 
