79 
Here also is placed the extraordinary Glass Rope 
(. Hyahnema 9 Gray), the axis of which is formed of nu¬ 
merous transparent siliceous fibres, slightly twisted to¬ 
gether so as to look like a rope of spun glass ; the fibres 
appear to be somewhat similar to the calcareous spicula 
of the Alcyonia. These corals are found with their 
tapering base inserted in a sponge, on the coast of Ja¬ 
pan. No animal, hitherto discovered, except the inha¬ 
bitant of this extraordinary substance, secretes pure 
silica. 
Cases No. 17 and 18 contain the family of Sponges 
( Spongiadce ). They resemble the corals of the last fa¬ 
mily in various particulars, but their animal nature is 
not distinctly made out. 
The Sponges found in collections are merely the 
skeletons of the living mass, entirely destitute of the 
gelatinous portion which constitutes the animal, if it be 
really of that nature. Some naturalists have considered 
these skeletons, or Sponges, as analogous to the stems of 
Antipathes, or Black Coral, and therefore the axes of 
zoophytes; and have fancied that, when alive, they were 
covered like the Antipathes, with an evanescent bark, in 
which they supposed the polypes to be situated. But 
recent observations on them in their living state have 
not verified this theory; for they have been found to 
be entirely destitute of any polypes, but living masses, 
covered with a gelatinous coat, and absorbing water 
through the small pores spread over its surface, and 
emitting it by the larger scattered holes called oscula ; 
and that though the fibres of many of the sponges 
greatly resemble the axes of the Gorgonise, in their 
chemical composition and organic structure, they 
nevertheless cannot be confidently pronounced to 
belong to the animal, rather than to the vegetable 
kingdom. 
The sponges have been divided into several genera, 
according to the structure of the skeleton. 
In the Common Sponge ( Spongia) the body is very 
elastic, composed of horny fibres anastomosing in 
every 
ROOM XI 
IN!at. Hist 
