No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 233 
the randplatte was covered by a precisely similar membrane, 
which was marked off from the randplatte by a deep furrow. In 
all such specimens the ectoderm of the randplatte was continu- 
ous at the edge of the latter with the calycoblast layer. These 
peculiar membranes gave every indication of having been origi- 
nally continuations of the randplatte; and I conclude that in 
the individuals possessing them, the extra-thecal part of the 
polyp had remained intact up to a certain time, but that then 
the whole lower portion of this part of the animal was cut off 
from the general gastric cavity. Deprived of its nutriment, this 
portion became membranous, and was infested by plant filaments. 
As the coral increases in size, the membranes are shed, leaving 
a large part of the theca bare. After the randplatte once be- 
comes restricted to the upper part of the skeleton, there is no 
more shedding of large pieces of tissue. But as the skeleton is 
constantly growing in height, we have to suppose that the rand- 
platte as constantly dies at its free edge, unless, indeed, we 
assume that the connection between the calycoblast layer and 
the skeleton is so slight that the randplatte is merely carried up 
with the growing skeleton. 
In the young Manicina, Figs. 41, 42 (4 in. diam.), the skele- 
ton is very immature, though the various parts of the adult 
skeleton can all be recognized. In this specimen there was a 
thin, flat, basal plate, uncovered at its periphery by the body 
wall. The skeleton above the plate was internal except at the 
points a and a‘, where the lower edge of the extra-thecal part of 
the polyp was notched, so that at these points the skeleton was 
bare for a short distance above the basal plate. Fig. 41 is 
through the cesophagus, Fig. 42 is below, and strikes the apex 
of the columella. Though some of the septa are still independ- 
ent at as low a level as Fig. 42, at a still lower level they all 
unite to form a theca, which on the right side of the directive 
mesenteries is very slightly developed, but on the left side is 
prominent. Two or three of the septa in the region where the 
theca is so slightly developed, exhibit the bifurcation of their 
peripheral ends which Lacaze Duthiers and Von Koch have 
described. In Fig. 42 indications of six primary septa are more 
or less evident, and in lower sections where the septa fuse with 
the columella they are easily distinguished. There are also six 
secondary septa to be made out in Fig. 42. These twelve septa, 
