18 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The disc has an undulating margin and is perforated by a central 
opening, having a diameter generally somewhat more than a third 
of that of the disc, and also by a single circular or oval row of 
8-12 holes, which lie between the central opening and the mar¬ 
gin. In addition to these there are occasionally a few smaller 
holes between this circular row and the margin of the disc. 
The leg of the calcareous table when completely formed is 80-98 /x 
in height, and is made up of four rods which are perpendicular to 
the plane of the disc. They do not arise from the outer rim of the 
disc, as in C. Ransonetti (Marenzeller), but from that part which 
lies between the central orifice and the row of holes surrounding 
it. The portion of the four rods attached to the disc comprises 
the original X-shaped spicule (Figs. 26-28), which is considerably 
arched across the central perforation of the disc, the convexity 
extending toward the surface of the body. 
Selenka (’67) described these spicules and figured one of them, 
but did not describe the leg of the completely formed table. 
Kingsley ( ? 81) apparently overlooked entirely the leg, though he 
figured accurately the two concentric rings of the disc. Semper 
(’68) gives an accurate figure of both parts of the calcareous 
table. 
Development of the calcareous tables. — The manner of develop¬ 
ment of these calcareous bodies from an X-shaped fundament is 
similar to that in all other known holothurians. If a piece of the 
integument of an immature specimen of Caudina, measuring perhaps 
5 mm. in total length, be stretched out to its natural dimensions 
upon a bit of cork, stained to show the nuclei, and mounted in 
balsam, calcareous bodies in different stages of development (Plate 3 , 
figs. 26-33) are found beneath the external epithelium, covering nearly 
the whole surface. The smallest X-shaped spicule observed (Figs. 
26, 26a) measured 23 x 27 /x diagonally; the body of the spicule, 
from which the arms extend, has a long axis of about 14 /x, and a 
thickness of 4-5 /x. As the spicule increases in size the body does 
not materially change in dimensions, but the arms increase in length 
till they measure about 20 /x long, with a corresponding increase in 
thickness, when a second branching (Fig. 29) occurs. A third set of 
dichotomous branches is then sent off, the central ones of which 
unite with their fellows from the adjacent primitive branches, 
whereas the peripheral ones send off the branches of the fourth set 
which, uniting, form the rim of the disc (Figs. 32, 33). 
