HALF AN HOUR WITH SPONGES. 53 



suck in and absorb. Simple though this " sponge- 

 flesh " appears to be, and really is, it is never- 

 theless provided with a simple means by which it 

 can keep up a constant and beautiful circulatory 

 system of sea-water throughout its entire structure. 

 Inside the sponge are a series of chambers communi- 

 cating directly with the external " pores." These 

 are all lined with the sarcole, or " sponge-flesh," and 

 here we find the granules ciliated, that is, having 

 hair-like processes formed by a simple prolongation 

 of the gelatinous tissue. These cilia keep up a 

 constant agitation, and by so doing create currents 

 in the water, which, passing through, nourish every 

 individual particle, and after doing so, pass out by 

 means of the " oscula." As Professor Huxley has 

 well remarked, the whole sponge represents " a kind 

 of subaqueous city, where the people are arranged 

 about the streets and roads in such a manner, that 

 each can easily appropriate his food from the water 

 as it passes along." Sponges are reproduced by the 

 detachment of little gemniules, or sarcode particles, 

 which pass into the open sea through the " oscula " 

 aforementioned. When first thrown off, each gem- 

 mule is furnished with cilia, by means of which it 

 moves about until it finds a convenient spot where 

 it can settle down into a sober sponge like its 

 ancestors. 



Sponges are among the oldest organisms of our 

 globe, for we find several genera fossilised in the 

 Silurian rocks. They are capable of being divided 



