KONGL. SV: VET. AKADEMIENS HANDLINGAR. BAND. Il4. N:o 6. 1 
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It may be as well here to make some remarks on the structure of a septum of this 
species, as seen, in thin sections and the more so, as the same septal structure prevails 
in most other corals, whether living or fossil, whether paleozoic or neozoic. In such 
a section there is visible a narrow central line, very thin, imbedded in a more dull 
white, compact endotheca. That central line is bent and twisted quite independently 
of the bendings and projecting parts of the ambient endotheca. Its independence of 
this and its being the chief and principal part of the septum is clearly indicated by 
the circumstance that it never is wanting in any septum, whether the dull white 
endotheca is present or not. Seen by transmitted light it is black and by reflected 
light it has a peculiar intense cream colour. At the exterior wall, where the stereo- 
plasmatic synapticula are mingled together into a continuous mass, there is only this 
narrow central line left as the sole independent portion of the septum and the rows 
of the small loopholes between the septa are the sole remnants of the once empty 
interseptal chambers. 
It is this central line and its two thicker sideportions, which have caused M. 
EDWARDS and so many other authors to start the view that a septum is composed of 
two lamin2e, the partition between them being at first empty and later filled up by a 
calcareous deposition. The true state of the things is, however, quite the reverse: the 
central, narrow stripe is the principal and original, simple septal lamina and the de- 
position around it is the endothecal structure, which I have called stereoplasma”), and 
which is formed not only around the septal lamina, but also fills the loculi with disse- 
pimental matter. What also strengthens my view of the composition of the septum, is the 
circumstance that as well in this species as in many others, the uppermost or, what 
is identical, the youngest border or edge all around the septum is a very thin lamina, 
wavy or bent in zigzag, and that the septum incereases in thickness only a little below 
this by deposition of stercoplasma. The discoveries of LACAZR-DUTHIRRS”) on the de- 
velopment of Astroides do not in the least favour the theory of a bilamellar septum. 
According to him the septum is at first deposited in a single line in the midst of a 
loculus, far from the muscular lamina and without any connection with them. It is 
true that sometimes weathered and exposed old specimens, especially fossil ones, look 
quite as if they had septa consisting of two lamin2e, but this is only owing to the 
central or original lamina having been dissolved and its place left empty. This again 
proves that there must be some intimate structural difference, not appreciable by means 
of the microscope or of chemical agents, and which causes one part of the corallum to be 
more easily destroyed than others. ”Thence it is conceivable that, as M. EDWARDS states, 
the two lamine of the septum are visible at the basal end of Flabellum and others. 
The septa of the third order deviate in Schizocyathus much from the others. They 
are wedged in between two septa of the second order, quite loosely, without any con- 
nection with them excepting the very scamty one which is effected by the common 
thin ecpitheca. They are best developed in the smallest specimens or low down at 
the bottom of the calicle, and decrease, as seen in PI. I, fig. 26, till they completely 
O 
1) Ofversigt af Vet. Akad. Förhandlingar 1873, p. 30 in sep. paper. 
?) Archives Zool. expérim. & gtnérale, I, p. 368. 
2 
K. Sv. Vet. Akad. Handl. Bd. 14. N:o 6 2 
