124 Mr. H. M. Bernard on the 
fractures in the direction of growth at any time show the 
appearance here called streaming; all sections across the 
streaming show what might be called, in contradistinction, a 
*¢ stationary ’’ reticulum. 
In the figures 3 and 4d (PI. II.) the artist—Myr. Percy 
Highly—has well shown by dots the usual appearance of the 
streaming layer. If these dots are thought of as pores in 
radial (septo-costal) plates lying in the plane of the paper, 
the reader will get a fair idea of what I believe to have been 
the origin of the streaming layer. The relative thickness of 
the streaming and of the thickening layer in figs. 3. a, 36, 3¢ 
should be reversed. The thinness of the streaming layer is 
probably indicative of the very early budding of the polyps. 
We have, then, in all Montiporans (with a few secondary 
modifications) a basal layer of reticulum streaming outwards 
(no matter how large or small the colony may be) and forming 
the growing edge, with or without the supporting epitheca. 
This streaming layer, which expands the corallum, for some 
reason or other cannot, as such, thicken it, and the new 
formation of coenenchyma for this purpose is in most cases 
sharply marked off from the streaming layer. An explanation 
of this thickening layer, shown in figures 3a, 36, 3c, as 
compared with 4 d, will be suggested later on. 
The thickening layer, wherever the epitheca accompanies 
the growing edge, is confined to the upper surface ; but if the 
growing edge is free, thickening layers may be added to both 
upper and under surfaces. These layers are derived from the 
threads or jagged edges of the surfaces of the streaming layer, 
On the upper surface they grow upwards at right angles to 
the direction of the streaming, and, uniting among themselves, 
form a filamentous reticulum. Similarly a layer of reticulum 
developed from points of the streaming layer bent down at 
right angles to that layer may cover the under surface. 
Whereas the upper layer may develop to almost any thick- 
ness and give rise to a very great variety of beautiful surfaces, 
the lower layer seldom thickens much; the individual threads 
soon tend to thicken, and thus to form a very dense reticu- 
lum, and sooner or later the epitheca grows out, covering 
over the calicles and leading to the more or less complete 
solidification of the lower surface. 
This description of the thickening and solidification of the 
lower surface does not apply to erect leaves or to branches 
which may be regarded as thick rounded leaves. In these 
cases the thickening layer may develop evenly on both sides 
of the leaf or all round the branches, and show all the surface 
specializations which in the horizontally growing specimens 
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