BONY STRUCTURE OF THE CORALLID^. 
219 
friend Dr. Arthur Farre, in his paper on the Structure of the Ciliobrachiate Polypi, 
in the Philosophical Transactions for 1837, p. 400, where he describes and figures 
them as occurring in the bases of the polyp cells. He conjectures that they are 
probably connected with the reproduction of the species. In many parts of the 
membranous structure of this coral, there appear numerous minute acicular double- 
pointed siliceous spicula, which do not exceed - 1 - 0 1 0 o °f an inch in length, and 
i2,5oo an inch in diameter. They are disposed without order, and are not to be 
found in every part of the membrane, but only in small groups at comparatively 
considerable intervals. Beside these minute spicula, there are others which occur 
sparingly dispersed amid the tissues, and which are of a different form and of much 
greater dimensions. The average size is of an inch in length, and ^ -o in 
diameter, and they are very much in form and proportions like a common brass 
pin, terminating at one extremity in a point, and at the other in a spherical head, 
and are well represented by the spicula in fig. 8, which were found imbedded amid 
the tissues of a species of Anthopora which I shall presently describe. These larger 
spicula were occasionally studded with a few tubercles, and in this as in other respects 
were so precisely similar to the spicula of this description, which are so abundant in 
some species of Halichondria and other genera of the Spongiadee, as to render it 
impossible to distinguish the one from the other, when separated from the respective 
bodies that have produced them. Upon examining the animal matter obtained from 
a species of Anthopora, the membranous tissue appeared as abundant as in the former 
cases, but somewhat denser in structure. The smaller tissue of vessels was present, 
although very indistinctly to be seen in parts between the membranes. The larger 
described vascular tissue was not detected in the portions subjected to examination. 
The principal features in this coral are the great abundance of large pin-shaped 
siliceous spicula, such as I have described as existing sparingly dispersed in the coral 
last referred to, and the occurrence of a profusion of the nuclei of Robert Brown, or 
cytoblasts of Schleiden, which were dispersed over all parts of the membranous 
structure, as represented in fig. 8. In some parts of the tissue they were in greater 
abundance than in others, and especially so when a cluster or fasciculus of vessels 
appeared to be seated beneath them ; and from this cause probably they also some- 
times resolve themselves into lines, curved or straight, consisting of eight or ten 
cytoblasts in succession. These interesting and curious organs were found imbedded 
in the membranous tissues of almost every coral that I submitted to examination. 
In the Anthopora they were nearly uniform in size, and about 2 W 0 °f an inch 
in diameter, but in other specimens they varied greatly in their dimensions. Their 
mode of disposition is also exceedingly various. Sometimes they occur singly and at 
long intervals ; at others, as in Anthopora, Plate XVI. fig. 8, in great abundance, and 
with but faint traces of order or arrangement ; while in other cases, as in Millepora 
alcicornis, they are disposed in circular groups, or in lines composed of a single series, 
which branch off and divide in such a manner as strongly to impress upon the mind 
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