160 



ACTINOZOA. 



up of a number of branching tubes, which are not, 

 as in all the preceding forms, perfectly calcareous. 

 In Cornularia and its allies a corallum, never 

 wholly tubular or of a firm calcareous consistence, 

 has yet been detected ; and in Sarcodictyon masses 

 of spicules only can be observed. In some species 

 of Alcyonidce proper, the spicules attain a com- 

 paratively large size, and become aggregated into 

 definite nodular masses. These ' dermosclerites \ 



Milne Edwards has shown 



kinds 



The for- 



mer are somewhat cartilaginous in consistence, 

 and have their surface studded with slight asperi- 

 ties. The irregular nodules are stronger and more 

 decidedly calcareous, presenting six faces, each, in 

 general, furnished with a tubercular enlargement, 

 which sometimes prolongs itself into a number of 

 spines, bearing on their sides other secondary 

 tubercles. By the coalescence of such masses and 

 the deposition of 



mor 



corallum 



nozoa, at length comes to be formed. In Alcy- 



onium 



? 



are 



not of large size, and are most conspicuous in the 

 column wall below the margin of the disc. Re- 

 turning to the Zoantharia we find, in the genus 

 Zoanthus, a spicular corallum still more feebly 



developed than that of Alcyonium. In many ot 

 the Sea-anemones no spicules have been observed, 

 though traces of a corallum are not, even in these, 

 absolutely lost. Finally among the Ctenophora 

 we in vain search for the faintest indications of its 



existence. 



From what has been said it were easy 

 that but little minute structure would be presen 



to infer 

 ted 



