BONY STRUCTURE OF THE CORALLIDiE. 
217 
of these large cylindrical vessels may be traced for a considerable distance, and 
many similar junctions of the large and small tissues be observed. They do not 
always join the larger so precisely opposite to each other as in the instance figured ; 
but in all the cases observed, the valves in each of the tissues were present, although 
not always in the same relative position in the large vessel, being sometimes on the 
contrary side of the mouths of the smaller ones to that represented in the figure. 
Occasionally, but very rarely, a valve is to be seen in the larger vessels where no 
junction with the smaller ones takes place. 
I have been unable to trace the large vessels to their natural terminations, but it is 
probable that they originate at the bases of the polyp cells, and that the valves with 
which they are furnished, were designed by nature to prevent the retrocession of the 
chyle, elaborated in the digestive organs of the polyps ; and this idea is strengthened 
by circumstances which I shall hereafter describe. 
The difference in the structure and characters of the larger and the smaller of these 
vascular tissues would seem to indicate that they have separate and distinct func- 
tions ; in the former we observe them maintaining a uniform diameter throughout a 
long course without once branching or dividing, while the latter immediately de- 
creases in size, dividing and subdividing until they terminate in vessels of extreme 
minuteness.. The valvular structure is also a character peculiarly distinctive of the 
larger system ; as there is not the slightest indication of such organs in the smaller 
vessels throughout the whole of their course, subsequent to their junction with the 
larger tissue. Several other corals that I examined exhibited this valvular tissue 
with very little variation in its character from that of Millepora alcicornis, but in one 
specimen ( Cellepora pumicosa ) it differs in so great a degree as to render a description 
of it necessary. Instead of being of an uniform character, and pursuing an unbroken 
course for a considerable length, as in Millepora alcicornis, it varied continually in 
its size, contracting in some parts to half or a third of the diameter that it exhibited 
at others, and especially so at the parts where the valves are situated, as represented 
at a, b, and c, fig. 3 . Sometimes, as at the point a, fig. 4 , it is terminated by an abrupt 
runcation and a slight lateral expansion. At each of these parts there is a valve 
and a new branch produced. In some cases, as at d, fig. 3 , there is but a single 
branch given off with the usual valves in the branch and main trunk ; and in others, 
as at b, fig. 4 , there is the same form of structure observed which is so characteristic 
of this description of vessel in Millepora alcicornis. The branches given off in all the 
cases figured from the Cellepora were not belonging to the fine complex system of 
vessels, but of the same nature as the parent ones, giving off secondary branches, as 
represented at c, fig. 4 , which have the valvular structure in every respect like the 
main vessel. I could not trace the connection between this valvular system of vessels 
and the minute contorted system with csecoid projections, although the latter was 
present in abundance ; but it may be fairly presumed from the result of the examina- 
tion of the Millepora, that such a junction does take place. About the same propor- 
mdcccxlii. 2 F 
