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 (PL II.) the artist — Mr. Percy 

 Highly — has v.'ell 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, 3 b, oc 

 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 ccenenchyma for this purpose is in most cases 

 sharply marked off from the streaming layer. An explanation 

 of this thickening layer, shown in figures 3 a, Sb, 3 c, 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 



