DESCRIPTION OF CORALS. 131] 
traces were noticed of curved lines parallel to the centre, marking probably re- 
newals of deposit: where, however, branches anastomosed, irregular extensions 
of the mantle apparently took place, and perfect, papillated exteriors were over- 
laid by layers either exactly moulded to them, or with irregular narrow inter- 
stices. These layers, of unequal thickness, were in some instances repeated 
more than once, as if certain parts of the animal membrane had successively 
perished, and permitted other portions to expand laterally: they proved also 
the destruction of the polypes belonging to the incrusted branch. The structure 
of the intertubular substance was rarely detectable, sections of older branches 
exhibiting a nearly compact body, and in those of younger portions it was gene- 
rally very obscure. Where best shown, it consisted of relatively coarse, rounded 
fibres diverging outwards, but variously anastomosed, and forming the internal 
equivalents of the surface papille. Between these fibres fine irregular elon- 
gated cavities occurred, and but for the rounded outline of the former, they 
would bear the aspect of small contorted channels permeating an homo- 
geneous substance. The fibres were penetrated by numerous microscopic 
tubuli; also internal representatives of the minute pores which beset the exte- 
rior papillae and the connecting matter. No larger foramina were detected in 
the surface. 
Many examples of immature, additional tubes were observed, either on the 
side of pre-existing, or in irregular extensions of intertubular layers. Among 
the former was a subdivisional case partially analogous to that mentioned in the 
brief notice on the development of marginal polype-cavities, but it differed in 
the separation having been effected by an irregular lamina unprovided with even 
rudiments of lamellz on the side towards the principal portion of the division, 
or that which included the central structure ; the severed part agreed, neverthe- 
less, with that of the marginal example in being semi-oval and traversed by ob- 
liquely-disposed lamellz. Other somewhat similar cases were noticed, but they 
were accompanied by more or less decided signs of great irregularities in the 
secreting processes, or of the polypes having been injured during growth. The 
interesting fractured surface exhibited in fig. 2b (Tab. I.) gave several instances 
of lateral developments, but all under nearly equivalent conditions, owing to the 
intersection having occurred deep in the lobes. Near the cross (X) is an outer 
smooth impression of a shoot at the very line of divergence. This case presents 
no irregularities in the lamella of the parent-tube at the side nearest the off- 
spring ; and the distance between the two polype-cavities at the base of the cast 
