ORDER ACTINOIDEA. 57 
consists of siliceous spicul, and has founded upon this character 
his genus Hyalonema.* 
51. Mr. B. Silliman, Jr., has been engaged in a series of analyses 
for this work, the detailed results of which will be given in the 
Appendix. We merely state here, that he has found in most of 
the calcareous corals examined, a small per-centage of magnesia, 
alumina, iron, silica, phosphoric acid, and fluorine, besides the car- 
bonate of lime, which constitutes, after separating the animal matter, 
from ninety-seven to ninety-nine per cent. The horny stem of the 
Gorgonia setosa afforded him a considerable proportion of alumina, 
besides phosphoric acid, some carbonate of lime, and ninety-three per 
cent. of animal matter. 
We have a sufficient source for the elements of these ingredients 
in the food of the polyps united with the waters of the ocean. 
Through their animal functions, such changes and recompositions 
take place, in the material thus received, as are required for the coral 
secretions. 
Ill. Repropucrion sy Bups—THE Compound STRUCTURE. 
52. In the preceding pages, on the Actinoidea, we have considered 
merely the simple polyp, in which reproduction takes place only by 
ovules, produced from the internal lamelle, and escaping by the 
mouth of the parent-animal. These polyps, in very many species, 
increase also by duds, and thus, from the single parent, perhaps but a 
fraction of an inch in size, zoophytes may spread their branches to a 
height of many feet. As we find the origin of the various forms of 
corals, in this power of developing buds, connected with some pecu- 
liarities in the animals themselves and their mode of growth, this 
subject is one of prominent interest. We may first consider simply the 
process of budding, and afterwards point out the different modes by 
which the budding process gives rise to the forms of zoophytes. 
1. THE Process or Buppine. 53. Buds proceed from different 
parts of a parent-polyp: those from the sides are called /ateral or 
inferior buds; and those from the upper extremity, either just exte- 
rior to the tentacles, or from the disk, are terminal or superior buds. 
The nature of the process is, in general, very similar to that de- 
scribed under the Hydroidea ()§ 15, 16). In lateral budding, a small 
protuberance appears on the side of the parent, into which the visce- 
* Proceedings of the Zoological Society of London, 1835, p, 62. 
15 
