566 DR. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 
cut off from any other communication with them than that which is afforded by the 
annular canals, with which each superficial chamberlet communicates at either end, 
by a passage which—thus traced out—is seen to be homologous with one of the double 
radial stolon-passages of 0. duplex , and therefore with the single radial passage of 
0. marginalis. The septa, i i, which divide the median portions, m m, of the 
successive annuli, are traversed by numerous passages, which, from the lateral 
obliquity of their direction (fig. III., 3scarcely show themselves in a radial sec¬ 
tion, although they debouch at the edge of the last annulus as marginal pores, mp. 
Notwithstanding this progressive complication in the structure of the shelly disks, 
there is no appearance of any corresponding specialisation in the character of the 
sarcode body: that of the typically “ complex ” form showing no other advance upon the 
very simplest, than is marked by the duplication of the sarcodic annuli, by the separa¬ 
tion of the superficial from the intermediate columnar sub-segments, and by the multi¬ 
plication of the oblique stolon-processes which connect these last with each other, this 
multiplication being obviously in relation with the increasing length of the interposed 
columns, which shows itself in the thickenum of the disk. The most marked increase 
in the complication of the animal body obviously consists in the duplication of the 
sarcodic annuli; and this may be readily conceived as a longitudinal splitting of each 
cord into two, with a persistence of adhesion at intervals, so that the two semi-annuli, 
when carried apart from one another by the interposition of the intermediate stratum, 
remain connected by the vertical sarcodic columns which traverse that stratum. The 
sub-segments which occupy the upper and under layers of surface-chamberlets are 
clearly shown, by their relation to the sarcodic annuli, not to be new productions, but 
to be homologous with the upper and under halves of the sub-segments that occupy 
the columnar chamberlets of the “ simple ” type; that homology, however, being so 
masked in the typically “ complex ” form by the displacement they have undergone, 
that it could not have been certainly recognised, but for the occurrence of those sub¬ 
typical forms which enable, the passage from the most “simple ” to the most “ com¬ 
plex to be continuously traced-out. 
I have been unable, after the most careful examination of the sarcodic bodies of 
0. duplex and 0. complanata, to discover any indication that this progressive complica¬ 
tion in the disposition of their parts, is accompanied by any such structural modification 
as might lead to the suspicion of differentiation of function. On the contrary, I find 
their substance to be everywhere of the same elementary character, consisting of a 
homogeneous protoplasm, that contains a large number of spherules of from 6 oV oth to 
~ 8 oV uth of an inch in diameter, sometimes crowded closely together, in other instances 
more dispersed, as shown in fig. 3, Plate IV. of my former Memoir (Phil. Trans., 
1856). These spherules, when subjected to pressure, break up into a number of 
pellucid corpuscles, which are usually of from 1 5 000 th to jo' o ooth of an inch in diameter. 
The absence of these spherules is a marked feature of difference in the protoplasmic 
