ORGANISATION OF SPONGES. 385 
The Porifera, or Sponges, were formerly supposed to belong 
to the vegetable kingdom, but their animal nature is now fully 
ascertained, for modern researches have proved that the soft 
glairy substance with which their skeleton is invested during 
life consists of “sareode,” similar to that which forms the soft 
parts of the Foraminifera and Polycystina. It is by this 
animated or organic gelatine, which can generally be pressed 
out with the finger, and in some species is copious even to 
nauseousness, that the solid parts of the sponge are deposited, 
and from it the whole growth of the mass proceeds. The 
framework or skeleton of the Porifera is usually composed of 
horny fibres of unequal thickness, which ramify and interlace 
in every possible direction, anasto- 
mosing with each other so as to 
form innumerable continuous cells 
and intricate canals, the walls of 
which in the recent sponge are 
crusted over with the gelatinous 
living cortex. La ie Single one or open cell, and 
Generally this fibrous mass is in- wounding fuer ee ae of 
terwoven with numerous mineral 
spicules of a wonderful elegance and variety of forms, for their 
shapes are not only strictly determinate for each species of 
sponge but each part of the sponge, it is believed, has spiculee 
of a character peculiar to itself. Sometimes they are pointed 
at both ends, sometimes at one only, or one or both ends may 
be furnished with a head like that of a pin, or may carry three 
or more diverging points, which sometimes curve back so as to 
form hooks. Sometimes they are triradiate, sometimes stellar ; 
in some cases smooth, in 
others beset with smaller 
spinous projections like the 
lance of the saw-fish. In 
many species they are 
embedded in the horny 
framework ; in others, as, 
for instance, in Tethea Needle-hke and starred spicula of a Tethea. 
Cranium, or in Halichon- ger wus ctater 7 
Cria, they project from its surface like a tiny forest of spears. 
They are generally composed of silex or flint, but in the 
