10 J.D. Dana on Zoophytes. 
whole axis is made up of spicule, or consists of a material resem- 
ing cork in texture. ji 
42. In the Melitzas the polyps grow obliquely upward, and 
their bases are directed downward instead of inward. The foot 
secretions form a layer at base, of this cork-like material; upon 
ding takes place, and the new polyps begin another layer at base. 
Thus an alternation of the two kinds. is produced, and the 
. 
rence in them of fluorine and phosphoric acid, was first detected 
in the food of the po yps, and in the ccean’s waters which 
are constantly bringing new portions of these mineral materials 
over the coral reefs through the action of the waves and the 
great marine currents.t There is no foundation whatever, as far 
nie acid springs occur in the vicinity of growing corals; and 
farther, there is convincing evidence to the contrary. Moreov 
of a sulphate or carbonate, since the elaborations of life may de- 
Compose and recompose according to the nature of the animal 
functions. 
Reproduction by Buds.— The Compound Structure. 
45. We have been considering in the preceding pages on the Ac- 
tinoidea, the characters of the simple polyp, its structure, repro- 
duction by ova, and its coral secretions. ‘The compound struc- 
ture exhibited by most coral-zoophytes, is a result of the addi- 
tional function of budding, and essentially in the same way as 
in the Hydroidea, By this simple means, all the various forms 
of zoophytes result. 
Many of the various shapes which these zoophytes assume, 
i known. ) 
common in collections. The hemispheres of brain-coral (Mean- 
drina), and also of star-coral (Astrea), are often met with, It is 
here, this Journal, i, ii Series, 189; ‘and also for some gedlosical deductions 
therefrom, ibid, ii, 88. ea 
fale ae eeatrence of fluorine ip sea-waier suggested by Mr. Silliman, asa 
result of bis investigations; and it has since een proved by actual analysis by 
Mr. G. Wilson of Edinburgh. (See this Journal, ii, ii Series, 115.) 1 z 
