55G 
DR. w. B. CARPENTER ON ORBITOLITES TENUISS1MA. 
in a fractured portion of the preceding zone which then formed the margin of the 
disk, it would seem to have been a special reparative addition. 
The whole cavitary system, from the primordial chamber to the marginal annular 
gallery, is occupied by a continuous sarcodic body of a dark olive-green hue (Plate 38, 
fig. 1). Although this body may be said to consist at any one moment of a multitude 
of sub-segments, connected together by annular and radiating stolon-processes, yet, 
from what we know of its semi-fluid condition in the living animal, we may pretty 
confidently surmise that this subdivision is by no means permanent, but that an 
interchange is continually taking place between the protoplasmic contents of the 
inner and the outer portions of the cavitary system, so that what occupies the central 
spire at any moment may be transferred in no long time to the marginal annulus, and 
vice versa. 
The extreme tenuity of this sarcodic body, and the transparence of the shelly 
laminae that invest it, have enabled me very distinctly to recognise, by light trans¬ 
mitted through the disk, the presence of nucleus-like bodies (Plate 38, fig. 2) of about 
1-1750th of an inch in diameter, imbedded in its substance. As might be expected 
from the consideration just stated, these corpuscles are very irregularly distributed. 
In the specimen here figured (Plate 38, fig. 1), two of the outer half-whorls of the 
‘ spiroloculine ’ centre (shown on a larger scale at b, b, b', b', fig. 4), are crowded with 
them ; while in a single chamberlet, c, of one of the interior annuli, there are as many 
as five. Elsewhere, on the other hand, they present themselves with less frequency, 
only one or two occurring in any single chamberlet (d, d, d), and a large proportion of 
the chamberlets being entirely destitute of them. The finding of these corpuscles in the 
highly composite sarcode-body of Orbitolites is an interesting extension of the discovery, 
of Dr. R. Hertwig, of corpuscles regarded by him as nuclei, in what I long since 
characterised as the “ reticularian ” type of Rhizopoda, of which the ordinary 
Foraminifera are the testaceous forms. This discovery was first made in the fresh¬ 
water Monothalamous Mikrogromia* and subsequently extended by him to various 
marine Polythalamia, such as Spiroloculina, Globigerinci , and Rot alia, \ and by 
F. E. Schultze to Quinqueloculina, Lagena, Polystomella, and Planorbulina.\ What 
is the function of these corpuscles in that indefinite extension of the protoplasmic 
body, and the multiplication of its segments, which is so remarkable a character of 
this type, is not yet apparent; but that they do not become the centres of distinct 
cells separated from each other by any limiting membrane, or even of permanent 
segments or sub-segments, may be regarded as certain. If the nuclear character of 
these corpuscles be admitted, the entire composite organism thus seems to 
present a most interesting link of connexion between the unicellular and multicellular 
types ; the absolute continuity of its protoplasmic substance entitling it to rank with 
* Arcliiv fur Mikrosk. Anat., Bd. x., Supplementkeft (1874) p. 1. 
f Jenaiscke Zeitschrift, Bd. x., 1876, p. 41, &c. J Arcliiv fur Mikrosk. Anat., Bd. xiii., 1877, p. 9. 
