186/,] DR. J. E. GRAY ON HYALONEMA LUSITANICUM. "121 



among the sclerobasic alcyonoid, and of Antipathes among the sde- 

 robasic zoanthoid jjo/i/pes. 



The siliceous spicules of sponges (as for example, the very elon- 

 gated filiform spicules of the genus Euplectella, which are most like 

 those of Hyalonema) are formed of numerous very thin concentric 

 coats formed of silica and horny matter ; but this is exactly the 

 structure of the axis of Goryonia (of the alcyonoid polypes) and of 

 Antipathes of the zoanthoid polypes. 



In Hyalonema the coats are siliceous, mixed with horny matter ; 

 in Gorgonia the coats are either almost entirely horny or of horny 

 matter mixed with a greater or less quantity of calcareous and sili- 

 ceous matters. Though the axes of the Gorgonia and Antipathes are 

 generally found with an expanded base, by which they are fixed to 

 marine bodies, the Pennatulce, which are free, have a fusiform axis, 

 like the separate spicules that form the coil of Hyalonema. 



I can only consider that the spicula of Hyalonema are the fusiform 

 axes of a coral which, instead of having one axis to the community 

 of polypes, has several coiled together like a rope, but separated 

 from each other by a layer of corium. 



The coil of the spicula in Hyalonema occupies the same position 

 and answers the same purpose (that is of supporting the canal) as the 

 axis of the sclerobasic alcyonoid and zoanthoid polypes — that is to 

 say, the axis of Gorgonia, Antipathes, and Pennatula. 



III. The spicules of sponges are only covered with sarcode ; while 

 the spicules of the Hyalonema are each surrounded by a layer of 

 corium exactly like the inner surface of the bark or corium of the 

 polypes. 



The zoologist who regards the coil of spicules as part of the sponge 

 considers the polypes on its surface a parasitic incrustation. H 

 this were the case, the parasites would only form a layer on the sur- 

 face of the coil without interfering with the coil of spicules on which 

 it is placed ; and the spicules of the coil, being part of the sponge, 

 would only be covered with the sarcode of the sponge, which, in the 

 sponge at the base of the Hyalonema, of which the coil is said to be 

 a part, is very small in quantity, scarcely enough to unite the spi- 

 cules of the sponge together, and scarcely visible on their surface. 

 In Hyalonema, on the contrary, the bark that covers the coil consists 

 of a thick hard fibrous corium covered with a thick external coria- 

 ceous coat, strengthened, as in Palythoa, with grains of sand or small 

 spicules. The inner layer of corium near the spicules or coil is 

 pierced by scattered small spicules ; and the corium extends within 

 the coil, surrounding each of the spicules with a thin fibrous coat, 

 uniting them all into one mass of a much m.ore solid and highly or- 

 ganized texture than the sarcode of any sponge I have examined. 



The zoanthoid polypes that form the bark on the coil of spicula 

 differ from those of the genus Palythoa and all other allied genera in 

 having the inner coat of their polype-cells and the base from which 

 tliey spring pervaded with siliceous spicules, similar in sha])e, but 

 smaller and much shorter than the spicules of which the coil is formed. 



