ofi Edinburgh , Session 1880 - 81 . 223 
is penetrated, though minute, being quite large enough to be at 
once recognised by the use of a lens. The precise appearances 
presented by these canaliculi in thin slices, vary according to the 
direction in which the section has been taken. Thus, in sections 
taken transversely to the eorallites (fig. 2, a), the tubuli are cut in 
Fig. 2. — A, Transverse section of a corallite of Tubipora musica, Linn., taken 
at tlie level of one of the connecting-floors, enlarged twenty times, showing 
the tubuli of the wall, b, Portion of the surface of one of the connecting- 
floors, enlarged twenty times, showing the external openings of the tubuli 
of the skeleton, c, Fragment of the corallum of Tubipora, enlarged 
sixty times, showing the composition of the skeleton out of spicules. The 
figure is taken from a thin section which divides the tubuli of the skeleton 
at right angles. 
the direction of their length ; and the same is true of sections 
which are taken parallel to the eorallites, but which lay open the 
visceral chambers of the latter. On the other hand, sections through 
the walls of the eorallites taken parallel to the visceral chamber, 
and sections of the connecting-floors taken parallel to their upper or 
lower surfaces, cut the canaliculi at right angles, so that these 
appear as minute rounded or oval pores in the skeleton. 
The only other points connected with the minute structure of the 
skeleton, as revealed by thin sections are, — firstly , that it is easy 
to observe that the corallum is made up, as pointed out by Pro- 
fessor Perceval Wright, of a network of irregular fusiform spicules 
fused together (fig. 2, c), and secondly , that the marked red color- 
ation of the skeleton resides chiefly in outer layer of the thecae, the 
inner layer being nearly or quite white. 
VOL. xi. 2 F 
