280 THE MICROSCOPICAL NEWS. 
bottom of the animal kingdom—to those realms where heads, limbs, 
bones, muscles, mouths, vessels, nerves, lungs, and organs of sense, 
or of anything else for that matter, are left far behind, and the 
animal or zooid, if it possesses what may without flattery be called 
a shape, may be congratulated on its superiority over some of its 
near relations. 
The material known in commerce as sponge is obtained by 
divers from the sea-bottom in the neighbourhood 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 communicate 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 eratode (Gr. keras, horn ; eidos, 
form). In a living sponge this cannot be made out, for the skele- 
ton is then covered 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 lamellee and leaving only 
a series of narrow, branched canals, the smaller branches of which 
communicated with a number of microscopic openings called 
“‘nores” 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 carmine—has been 
added, it may be observed that currents of water are constantly 
flowing into these pores, while other currents are streaming away 
from the larger apertures, called oscw/a (Lat. dim. of os, mouth). It 
is thus evident that there is a constant circulation of water entering 
the sponge by the pores or z7ha/ent apertures, traversing the various 
channels in the substance of the sponge, and emerging from the 
oscula or exhalent apertures. 
Sections of fresh sponge display the fact that the slimy substance 
—the so-called sponge flesh—consists of an assemblage of nucleated 
corpuscles or sarcoids, about zgy5g OF ypgp Of an inch in diameter, 
and of irregular and inconstant form. Each consists of a speck 
of colourless protoplasm, the semi-fluid granular interior of which— 
the endosarc (Gr. endon, within; sarx, flesh) passes into a firmer 
clear outer layer—the ecfosarc (Gr. ehtos, outside). In the endosarc, 
besides the nucleus there is sometimes a little cavity—contractile 
vesicle—endowed with the power of rhythmic dilation and con- 
traction. The sarcoid has the power of changing its form by 
the protrusion of blunt processes—from any part of its body, and 
