280 



The coral, as it is usually seen, consists of three distinct portions, 

 of very different texture and appearance — the axis, bark, and the 

 sponge. 



The axis is formed of a considerable quantity of transparent glass- 

 like fibres, slightly twisted from right to left into a spiral rope- 

 like bundle 18 to 20 inches in length and 3 or 3| lines in diameter 

 at the lower part, where the fibres are most closely applied to each 

 other, and whence the specimen gradually expands upwards to a dia- 

 meter of double that extent. 



The part above this tapering base is in different specimens covered 

 to a greater or less extent (and evidently in the perfect state is en- 

 tirely) with a kind of leathery bark, with large truncated nipple- 

 shaped scattered tubercles, having flat crowns with radiating grooves 

 and a central depression. 



The base of the transparent rope is (in one specimen) as it were 

 inserted into an irregular mass of a very loose spongy substance, to 

 which it is very firmly attached ; and in passing through which it 

 gradually tapers to about half the size of the narrowest portion of 

 the exposed part, and finally terminates in a truncated pencilled base 

 of very fine capillary fibres. In general, the specimens are withdrawn 

 from this spongy base, and the lower part of the axis is cleaned ; but 

 I think it is evident that they all are attached to such a sponge in 

 their natural state. 



The bark is formed of two distinct layers : the outer having the 

 appearance of an aggregation of grains of sand united together by a 

 small quantity of animal matter ; the inner portion having imbedded 

 in its substance numerous very fine capillary fibres of precisely 

 similar texture to those which form the axis of the coral, but of 

 much smaller size ; and this portion of the bark evidently extends 

 between and invests each of the fibres of the rope-like axis. 



The fibres which form the axis are perfectly transparent, colour- 

 less, and moderately flexible, resembling in appearance those of 

 gpun glass or very clear bristles. They vary in thickness from half 

 a line to the diameter of a very fine hair. In the middle portion 

 they are nearly cylindrical ; within 2 or 3 inches of the tip they 

 gradually taper to half their former diameter ; externally they ap- 

 pear to the naked eye smooth and polished, but as if furnished with ■ 

 numerous internal cracks taking different directions. Under the 

 microscope there are seen many close-set superficial annular grooves, 

 which become more evident near the tips, where they assume the 

 form of raised belts most prominent below, and giving a somewhat 

 irregular outline to the surface. Internally they are solid, and 

 formed of very numerous, very thin, concentric coats, as may be 

 seen by breaking them transversely, when, instead of presenting a 

 straight fracture, the coats appear of different lengths, in consequence 

 of their yielding at different intervals. If this fracture is minutely 

 examined under a lens, each of its component laminae is found to 

 present numerous concentric lines, showing it to be formed of several 

 plates. But this structure is most evidently seen on applying the 

 end of one of the broken fibres to the flame of a spirit lamp, when 



