182 Tue Microscope. 
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Selections, 
SPONGE. 
The material known in commerce as sponge is obtained by 
divers from the sea bottom in the neighborhood of the Greek 
Archipelago, the Bahamas, and other parts of the world, but it 
is not the whole animal but only a supporting skeleton from 
which all the living matter has been removed by washing, 
squeezing, and bleaching in the sun. If a piece of this sponge 
be examined with the naked eye there will be seen numerous 
large, more or less circular openings leading into canals which 
branch and penetrate the sponge in all parts and freely com- 
municate with one another. A simple lens of high power will 
show that the substance of this skeleton is composed of an open 
feltwork of curling and branching fibres of a horny substance 
called keratode (Gr. keras, horn; etdos, form). In a living 
sponge this cannot be made out, for the skeleton is then cov- 
ered with a slimy material and only the larger openings are 
then visible. Sections of the living sponge in any direction 
would show that this same slimy substance pervaded the whole 
interior, covering all the fibres and lamellz and leaving only 
a series of narrow, branched canals, the smaller branches of 
which communicated with a number of microscopic openings 
called “ pores” in the outside of this gelatinous mass. 
If a healthy sponge be examined in some of its native 
water, to which some finely-divided solid substance—say car- 
mine—has been added, it may be observed that currents of 
water are constantly flowing into these pores, while other cur- 
rents are streaming away from the larger apertures, called 
oscula (Lat. dim. of 0s, mouth). It is thus evident that there 
is a constant circulation of water entering the sponge by the 
smaller pores or znhalent apertures, traversing the various 
channels in the substance of the sponge, and emerging from 
the larger oscula or exhalent apertures. 
Sections of fresh sponge display the fact that the slimy 
substance—the so-called sponge fesh—consists of an assem- 
blage of nucleated corpuscles or sarcoids, about zv0 or svvo of 
