Dr. J. E. Gray on the " Glass-Rope " Hyalonema. 293 



show that any spicula of a true sponge are like the spicula that 

 form the axis of the coral. They certainly have little affinity 

 to the elongated siliceous spicula of the genus Alcyonellum or 

 Euplatella, with which they have been compared. 



The chemical part of the question I do not think of much 

 importance : we know so little of the power of animals to secrete 

 different substances. It is true that Hyalonema is the only 

 Zoanthariau yet discovered that secretes siliceous spicula ; 

 but if the marine and freshwater sponges secrete both calca- 

 reous and siliceous spicula, and a horny axis more or less hard- 

 ened with calcareous matter, and the Alcyonaria and Zoantharia 

 secrete a horny axis more or less hardened with calcareous 

 matter and abundance of calcareous spicula, why should we say 

 that these much more highly organized animals have not also 

 the same power as the sponges to secrete from the sea-water 

 silica, and therefore that a Zoantharia-polype that lives on a 

 siliceous axis is a parasite, especially when we find that this 

 Zoantharian polype has its bark and polype-cell strengthened 

 by siliceous spicula, some of them exactly similar in form and 

 structure to the spicula of the axis, which must have been 

 secreted by the animal ? And therefore it is, to my mind, most 

 unphilosophical to believe that the spicula of the axis are formed 

 by the sponge, and the similar spicula in the polypes formed by 

 the animal which the advocates of this theory regard as a para- 

 site having only an accidental connexion with the axis. 



The discovery of a species of Hyalonema on the coast of Por- 

 tugal has proved that there is a species of the genus (and a most 

 distinct one) that secretes siliceous spicula exactly like the spi- 

 cula of the Japan species, that has no sponge attached to it or 

 forming part of its body ; so that it cannot be the " cloacal sys- 

 tem '^ of a sponge that does not exist. 



Professor Max Schultze, who regards the bark and polype of 

 the Japanese species as a parasite, describes it as a species of the 

 genus PoUjthoa, under the name of Polythoa fatua ; but it dif- 

 fers from all the species of the genus Polythoa that I have ex- 

 amined in having the parietes of the polype-cells streugthened 

 with siliceous spicules which are exactly similar in structure and 

 form to the spicula of the axis. 



This peculiarity, which I should consider conclusive that the 

 axis is formed by the same animal as the bark, is common to 

 the Japanese and Portuguese species. 



Professor Barboza du Bocage observes : — 



" Le corium polypigerum et les polypes sont formes de plu- 

 sieurs tissus en couches superposees, dans lesquels on trouve 

 une quantite tres-consid^i'able de spicules siliceux, dont les 

 caracteres morphologiques variant pour chaque couche. 



