582 
G. HERBERT FOWLER. 
such numbers as often to completely obscure the true endo- 
derm, with which they of course have no connection. While 
accepting v. Koch’s theory as to the origin of the theca from 
fusion of the septa, he differs from it in some details, regarding 
the “ sutures ” as merely cracks artificially produced in the 
corallum. Septa and tentacles both entocoelic and exoccelic; 
mesenteries and their muscles arranged as in Actinia; for 
further details, which are very thoroughly worked out, his 
paper should be consulted. One point of importance deserves 
mention ; between the corallum and the structureless meso- 
derm-lamella which overlies it immediately and was generally 
understood to secrete it, v. Heider detected certain cells, for 
the most part scattered, but in some places forming a definite 
layer. To these he gave the name calycoblasts, and assigned 
the function of coral-secretion ; with great justice, as later 
researches proved, though their origin was a matter of doubt 
till cleared up by v. Koch. 
The latter, in a paper on the development of Astroides 
calicularis (9), brought into notice the following facts. 
When first fixed, and before the secretion of the skeleton has 
commenced, the embryo is plano-convex, and its ectoderm may 
be divided into two regions, corresponding to its surfaces, the 
plane disc of attachment, or basal ectoderm, and the convex 
portion or lateral ectoderm, the centre of which is iuvaginated 
as the stomodeeum. The skeleton first appears as sm-all pellets 
of calcium carbonate lying between the basal ectoderm 
and the foreign body to which the embryo is 
attached, and is therefore outside the animal, and conse- 
quently the result of secretion by the ectoderm. 
As the corallum is always described in text- books as a product 
of the mesoderm, this observation cannot be too strongly 
insisted upon. These pellets become, first a ring-shaped disc, 
then a complete disc lying between the basal ectoderm and the 
foreign body to which the embryo is attached. Where septa 
are to be formed the three body layers, endoderm, mesoderm- 
lamella, and basal ectoderm, rise upwards as a fold into the 
ccelenteron ; and as they rise, coral is deposited beneath them 
