230 WILSON. [Vou. IL. 
through such larve, after the lime has been removed by acid, 
give figures like Fig. 38, though in many individuals the ecto- 
derm was torn in freeing the larva from the bottom of the dish. 
In Fig. 38 the cells of the basal ectoderm radiate toward a com- 
mon centre. There seems to be an effort on the part of the 
more peripheral cells to share in the secretior. of the central 
patch of homogeneous substance shown in the figure. This 
homogeneous substance is the animal basis of the nascent basal 
plate. It exhibits no structure, but stains deeply with hzema- 
toxylin, and in its general appearance impresses one as a very 
much thickened cuticle. I was not able to trace the develop- 
ment of the skeleton any further. 
The fully formed skeleton may very conveniently be studied 
in young polyps, which have not begun to multiply asexually. 
Ground sections of the skeleton are of some use, but witha 
little care the polyps may be decalcified so that the skeletal 
layer of tissue retains with great exactness the shape of the 
skeleton. Figs. 46, 50, and 56 are from young J/anzcznas about 
one-third inch in diameter. Fig. 46 is part of a transverse section 
through the line a in Fig. 50 (oe. ec. is the ectoderm of the peris- 
tome ; ec. that of the lateral body wall). Were the section complete, 
it would show twelve primary, twelve secondary, and twenty-four 
tertiary pairs of mesenteries. At this level the secondary mes- 
enteries are complete ; a little lower down they are incomplete. 
In going down through a series of sections, the tertiaries run 
out before the lip of the cesophagus is reached. In Fig. 50 the 
line 3 marks the free edge of a tertiary mesentery. The theca, 
7h., divides the mesenteries and ccelenteron into peripheral and 
central portions. The septa, S., are all entoccelic; 2.2, lie be- 
tween the two mesenteries of one pair, and not between two 
adjacent pairs. The size of the septa varies with the rank of 
the mesenteries between which they lie. On the outer surface 
of the theca are the longitudinal ridges, C., or costa, which 
appear to be merely the peripheral prolongations of the septa. 
The edges of the septa are finely and regularly toothed. This 
is shown in the radial section, Fig. 56, which is taken through 
one of the coral septa. In Figs. 50 and 56 the relations of the 
columella, Co/., to the theca and septa are shown. In the 
former figure, through a mesentery on each side and conse- 
quently between two septa, a deep depression separates the 
