38 
If, tlierefore, wc dismiss such an arrangement of these important 
structures, liow is it tliat on longitudinal fracture the exterior of the various 
corallites has usually been supposed to he on view. According to the authors 
just referred to, such is not the case, and they have advanced the following 
ingenious explanation to account for it. Sj^eaking of the peripheral region 
of a Monticuliporoid coral, they say that longitudinal severance always takes 
place along the primordial wall, the latter adhering to one side of the fracture, 
the secondary thickening retaining its connection with the other side of the 
break. In the axial zone fracture takes place in the same manner, hut there 
T)eing little or no secondary thickening the other side of the break exposes 
“ the smooth internal cast of the adjoining individual.”^ Aiipearances pre- 
sented by our Stenoporce seem to me exj)licahle only on this supposition. 
The wall in freshly-fractured specimens appears as a thin pellicle-like 
substance of light colour, and peels off as such. In S. crinita this peculiarity 
is so marked that when combined with the stratified condition of the corallum 
the corallites of a given growth-stage break off as individual disjointed hexa- 
gons, octagons, or polygons, as the case may he. The presence of intermural 
gemmation in Stenopora, almost exclusively, would lead us, to some extent, to 
expect the exposure of the exterior of the corallites on fracture, and not, as 
in Chcetetes, in which llssiparity exists, the interior. Prom these combined 
causes, therefore, it is very difficult to account for the appearance of the 
interior as in Stenopora, unless it he by the above hypothesis. A condition 
of preservation which would appear to go far to hear out this view occurs in 
S. crinita, in which the longitudinal surfaces of wdiat Waagen and "VYentzel 
would call the internal casts of the tubes are invariably marked by the 
impressions of downwardly-directed crescentic imbrications of microscopic 
size. These, I believe, are the impressions of the superimposed conical layers 
of sclercnchyma composing the moniliform annulations of the walls, left 
after fracture, as explained by the authors above quoted. 
The structure of thickened portions of the walls is identical, whether 
the section betaken from the axial region, as in S. crinita,ov the peripheral zone 
of another form, and the polygonal outline becomes lost. The ti'ansition 
from the dark, hair-like proper wall (PL VII, Pigs. 2 and 3) to the mass of 
sclerenchyma forming the thickened wall is always abrupt, hut the moment 
this has taken place the structure becomes well exemplified, the sclereu- 
chyma or concentric tibro-laminar deposit, probably representing the ohliquely- 
cut edges of the superimposed layers of which the thickened annulations arc 
* Ibid., p, 8G4. 
