76 Dr. G.C. Wallich on the Process of 
intermediate space, such as would necessarily exist were the 
first two layers not secreted in contact. Hence it follows, that, 
after the deposit of the two primary layers (by the surface of the 
stolon and of the vacuolar cavity, as seen in fig. 2), all subsequent 
layers must be evolved from these surfaces in opposite directions 
—that is to say, centrifugally as regards the outer series, and 
centripetally as regards the inner one. And it may be stated 
that the growth of every sponge-spicule takes place in two oppo- 
site directions between its axis and periphery, and that every 
spicule presents an axial tube (or the remains of such tube), 
which was originally occupied by the vacuolar stolon around 
which its several layers were deposited. 
I shall now endeavour to show that, with the exception of one 
group of organisms which constitute the true connecting link 
between the Sponges and the Rhizopods, the process of mineral 
deposit in the latter class of Protozoa takes place so differently 
from that just described as prevailing in the former, that it fur- 
nishes a most important distinctive character between the two 
classes. 
If we leave out of the question the genera Polytrema, Carpen- 
teria, and Dujardinia, which are still sub judice, and restrict the 
term “spicule” to structure identical im its mode of formation 
with the spicules of the Sponges, no spicular growth has hi- 
therto been met with amongst the Foraminifera. The point for 
decision is not whether the spicules found in these genera are 
true sponge-spicules (for of that fact there is no doubt), but how 
they came there,—my argument being that, masmuch as they are 
undoubtedly true spicular growths, they cannot belong to, or be 
formed by, Foraminifera, and must consequently be of ento- 
zootic origin. 
Figure 5 is intended to illustrate the order in which the suc- 
cessive layers of calcareous matter are formed in a shell of the 
Globigerine type, Pc representing the primordial chamber, 
v T the first layer of shell secreted from the sarcode-surface with 
which it is in contact ; s, s, s, pseudopodial stolons traversing the 
shell through the larger foramina, and terminating at times, but 
not necessarily always, in pseudopodia; p, p, p, pseudopodia 
taking their rise from an external layer of sarcode (or chitosare, 
to be described immediately), and, in like manner with the 
pseudopodial prolongations of the stolons, not always in direct 
communication with the sarcode-mass within the chambers; 
and, lastly, a, the aperture of the chamber. 
s c represents the second chamber; the letters 1’ 1 the first 
layer of shell, as in the primordial chamber; s,s, the stolons, 
with the large foramina for their exit; p, p, p, pseudopodia, in 
this case springing directly from the sarcode-mass of the cham- 
