552 



SPICULES OF A1.CYONIA*. HELIANTHOIDA. 



tion that give a Black Ground, on which they stand out with 

 great brilliancy, especially when viewed by the Binocular Micro- 

 scope. They are, of course, to be separated from the Animal sub- 

 stance in the same manner as the Calcareous spicules of Sponges 



(§ 408); and they 

 Fig. 284. should be mounted, 



like them, in Canada 

 Balsam. — The 

 Spicules always pos- 

 sess an Organic basis ; 

 as is proved by the 

 fact, that when their 

 lime is dissolved by 

 dilute Acid, a gela- 

 tinous-looking resi- 

 duum is left, which 

 preserves the form of 

 the spicule. 



427. Of the order 

 Helianthoida, the 

 common Actinia or 

 'Sea-Anemone' may 

 be taken as the 

 type ; the individual 

 Polypes of all the 

 Composite fabrics included in the group being constructed upon 

 the same model. In by far the larger proportion of these 

 Zoophytes, the bases of the Polypes, as well as the soft flesh that 

 connects-together the members of aggregate masses, are consoli- 

 dated by Calcareous deposit into Stony Corals ; and the surfaces of 

 these are beset with cells, usually of a nearly-circular form, each 

 having numerous vertical plates or lamellce radiating from its 

 centre towards its circumference, which are formed by the con- 

 solidation of the lower portions of the radiating partitions, that 

 divide the space intervening between the Stomach and the general 

 integument of the animal into separate chambers. This arrange- 

 ment is seen on a large scale in the Fungia or ' Mushroom-Coral ' 

 of tropical seas, which is the stony base of a Solitary Anemone- 

 like Polype ; on a far smaller scale, it is seen in the little Caryo- 

 phyllia, a like Solitary Polype of our own coasts, which is scarcely 

 distinguishable from an Actinia by any other character than the 

 presence of this disk, and also on the surface of many of those 

 Stony Corals known as ' Madrepores ; ' whilst in some of these the 

 individual Polype-cells are so small, that the lamellated arrange- 

 ment can only be made-out when they are considerably magnified. 

 Portions of the surface of such Corals, or sections taken at a small 

 depth, are very beautiful objects for the lower powers of the Com- 

 pound Microscope, the former being viewed by reflected and the 



a, Spicules of Gorgonia guttata. 

 jr, Spicules of Muricea elongata. 



