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 
Zoantharian yet discovered that sccretes 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 Aleyonaria 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 Polythoa, 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 strengthened 
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 formés de plu- 
sieurs tissus en couches superposées, dans lesquels on trouve 
une quantité trés-considérable de spicules siliceux, dont les 
caractéres morphologiques varient pour chaque couche. 
