5A ZOOPHYTES. 
secretions are nearly or quite absent immediately about each polyp- 
pore, in order that these parts may be flexible to admit of the animal’s 
Fig. 22. contracting and expanding itself; 
i \ elsewhere they are more or less 
\ abundant, according to the species. 
i 
[ / In the genus Tubipora, the spe- 
/ , ne 4 cies form a thin calcareous tube 
Uy, for each polyp, smooth within, as 
ih \ ‘i ~ well as without, yet perforated by 
minute pores. 
48. Among the Actinaria, the principle, that the calcareous and 
fleshy lamelle have a general correspondence in number, leads 
to important distinctions in the coralla. Madrepores, on this prin- 
ciple, can never have over twelve rays to their cells, and the number 
is usually from six to twelve; while the Caryophyllia and Astrea 
tribes have an indefinite number. ‘The two tribes just mentioned are 
distinguished in their coralla by another character depending on the 
structure of the animals, as explained in § 42. The lamella of the 
stars in an Astrea, and the allied corals, extend through the intersti- 
tial spaces between the cells, striating lamellately the surface ; while 
in the recent species of the Caryophyllia group (and also the Madre- 
pores), these spaces are smooth, granulous, or irregularly porous, 
instead of lamello-striate. Besides, in the former, the calcareous 
lamelle are united by numerous transverse dissepiments, which, 
when oblique, as in plate 11, figure 4¢ (showing a vertical section of 
an Astrea), they cause the star in a transverse section to be divided 
into numerous cellules (fig. 4d); but, if horizontal, or nearly so, as in 
plate 10, figure 2a, they do not show their edges in a transverse view, 
and the star appears simple. In the recent Caryophyllide, there are 
seldom any cross dissepiments, and in the few cases in which they 
are observed, they are distant, being separated by longer intervals 
than the breadth of a lamella. 
49. I oot-secretions. ‘The foot-secretions appear to be entirely inde- 
pendent of the tissue-secretions. The former are often horny, when 
the latter are calcareous, and when they occur together they consti- 
tute separable layers, one enveloping the other. 
The united polyps of a branch have their mouths opening outward 
on every side, while the bases are directed inward towards a common 
central or axial line. The simultaneovtfs secretions of the bases, there- 
fore, must necessarily produce a solid axis to the branch. 
