BONY STRUCTURE OF THE CORALLIDjE. 
221 
and in fig. 4 . These vessels appear to be part of a system of minute vascular tissue 
peculiar to these organs, as they differ in character from the minute vascular tissue 
that we have before described as prevailing almost universally in the animal matter of 
the Corallidse, being furnished with valves or diaphragms at regular intervals. But 
the most singular circumstance is that they appear to demonstrate the fact, that cy- 
toblasts are not only concerned in the production of the cellular structure, but that 
they are also the direct originators of the vascular tissue, for in this case we observe 
short branches given off at nearly right angles from the minute vessels, and at the 
apex of each of these there is seated a small cytoblast, not exceeding 71x3 of an 
inch in diameter, but very considerably larger than the branch that supports it, which 
measured but of an inch in diameter. Other small cytoblasts are seated 
upon the vessels, as shown in fig. 4 , which represents one of the sacs with the ac- 
companying vessels and cytoblasts, as seen with a microscopic power of 800 linear. 
The vessels are not attached to the sacs throughout the whole of their course ; con- 
siderable portions of them are floating freely between the organs ; and branches from 
these free vessels are often to be seen passing in a very singular manner half round 
the outer circle of the cytoblast at the apex of the sac, and, upon quitting it, proceed- 
ing to another and embracing it in a similar manner : indeed, the apices of by far the 
greater number of them are thus visited by branches of the vessel. It is difficult to 
imagine the purpose of the connection between them, but it is evident that the two 
organs are connected in their operations, whatever they may be. 
The result of the examination of two specimens of Nullipora from Australia, which 
appeared to be of the same species, was exceedingly interesting. The cellular struc- 
ture was developed in the most perfect and beautiful manner in both of them. The 
greater number of cells were empty, transparent, and in a slight degree larger at one 
end than at the other. At the smaller extremity of each there is most frequently a 
cytoblast, which is usually as pellucid and transparent as the walls of the cell, but in 
other cases it is full of a brown and indistinctly granulated matter, as represented in 
Plate XVII. fig. 5 , which exhibits a view of the ends of the cells with the cytoblasts 
in this state, while fig. 6 represents a longitudinal view of the same structure in its 
transparent state. In this position the cytoblasts are not at all times to be seen. 
In the second of the specimens examined, there was an abundance of fine mem- 
brane, with a quantity of a glutinous-looking matter adhering in irregular patches to 
its surface, and of the complex vascular tissue with the ceecoid appendages ; thus as- 
similating the general character of its structure in a very close degree to that of the 
true Corallidse. Although in many parts of its cellular structure it exhibits an ap- 
pearance very much like that of some succulent vegetables, yet there are others in 
which this similarity does not obtain, and where the cells are so loosely disposed as to 
preserve nearly a cylindrical form (Plate XVII. fig. 7 ), and to assume very much the 
appearance of the cells of the fatty tissues in the higher class of animals : while the 
perfect identity of the character of the vascular tissue with that of the true corals. 
