PHILOSOPHICAL TEANSACTIONS. 
I. Besearches on the Foraminifera. 
WiLLmi B. Caepentee, M.D., F.B.S., F.G.S., &c. 
Eeceived June 17, — Eead June 17, 1858. 
PAET III. 
ON THE GENEEA PENEEOPLIS, OPEECHLINA, AND AMPHISTEGINA. 
1 1 9. liS^ my preceding memoirs, I have shown that two very dissimilar types of structure 
present themselves among Foraminifera ; one characterized by its simplicity, the other 
by its complexity. In the former, of which Orbitolites, Orhiculina, and Alveolina are 
typical examples, the calcareous skeleton does not present any definite indications of 
organization, but seems to have been formed by the simple calcification of a portion of 
the homogeneous sarcode-body of the animal ; that sarcode-body is but very imperfectly 
dmded into segments, the communications between the cavities occupied by these 
segments being very free and iiTegular ; the form of the segments themselves, and the 
mode of their connexion, are alike inconstant ; and even the plan of growth, on which the 
character of the organism as a whole depends, though preserving a general uniformity, 
is by no means invariably maintained. In the latter, to which Cycloclypeus and Hete- 
rosfegina belong, we find the calcareous skeleton presenting a very definite and elaborate 
organization ; the several segments of the body are so completely separated from each 
other, that they remain connected only by delicate threads of sarcode ; each segment 
thus isolated has its own proper calcareous envelope, which seems to be moulded (as it 
were) upon it, and this envelope or shell is perforated with minute parallel tubuli, 
closely resembling those of dentine except in the absence of bifurcation or ramifica- 
tion; the partition-walls between adjacent segments are consequently double, and are 
strengthened by an intermediate calcareous deposit, which is traversed by a system of 
inosculating passages that seems properly to belong to it. The form of the segments, 
their mode of communication, and consequently the general plan of growth, have a very 
considerable degree of constancy ; and altogether the tendency is strongly manifested in 
MDCCCLIX. B 
