J. D. Dana on Zoophyies. ‘9 
corals. On this account the number of lamell (and correspond- 
ingly of tentacles) is usually some multiple of four, when the 
whole number exceeds twenty-four; and itis generally also a 
multiple of siz. Below this, the lamelle if over six are com- 
monly large and small alternately, or one alternates with two 
others that are alike ; and the number isa multiple of siz. ‘These 
are therefore all parts of one system. 'The Alcyonaria appear to 
belong to a different system, since they have eight equal tentacles 
and lamelle. saved 
The importance of number and size as a specific distine- 
tion is therefore obvious. In the species of a single genus or 
family, there is a relation admitting of limited variations, be- 
tween the diameter of the polyp and the number of its visceral 
lamella, and therefore of its calcareous lamelle when corallige- 
nous. As the number of tentacles and internal lamelle of a po- 
lyp increase as it enlarges, so it is with the lamelle of the coral- 
lum ; but the adult number is fixed. 
40. In the Alcyonaria, the internal secretions are in dissemi- 
nated grains or spicule, and when a solid tube is formed, it pro- 
ceeds from the aggregation of these grains. The difference in 
the microscopic structure of these spicule and the coral of the 
Actinaria has been stated in this Journal, i, ii Ser., 284. ‘There are 
many species that are wholly fleshy, others in which the grains 
oophyte is therefore still flexible ; and others 
that are firm and solid from their numbers and union. In the 
still flexible ; and as they grow upward, the tube at the same rate 
axis, which is the result of basal secretions. The polyps have 
their bases inward, and of course an axis should result from their 
united secretions. This axis is very similar in nature to the horn 
, It is also calcareous at times as in 
the common red or noble coral of commerce ; for this material 
forms the axis of a zoophyte, and is covered, when alive, with a 
layer or crust of brilliant polyps. ‘This fact accounts for its being 
solid in texture without the cells of ordinary coral. 
concentric structure may sdmetimes be distinguished in these 
axes; andat times the centre (the first secretions of the younger or 
apical polyps of a branch) is open om ‘a some species the 
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