14 MECHANICAL FUNCTIONS. 



tinued to watch the same orifice, at short intervals for 

 five hours, sometimes observing it for a quarter of an 

 hour at a time, but still the stream rolled on with a con- 

 stant and equal velocity." 



12. The water thus poured forth in a perpetual stream 

 from these apertures, is received through the millions of 

 pores which pervade the sponge in every direction, and 

 by this means it is that the animal is nourished. Even 

 fish of several pounds weight will live for weeks, or per- 

 haps months, upon no other nourishment than what is con- 

 tained in sea-water, so that the sustenance of the sponge 

 by such means presents nothing, uncommon. 



13. The mechanism by which these currents of water 

 are constantly produced, is involved in obscurity. It is, 

 however, supposed to consist of cilia, or small hairs lining 

 the inner surfaces of the tubes, the motions of which propel 

 the water through them. 



14. These currents are readily made apparent by pla- 

 cing the living animal in a shallow vessel of sea-water, and 

 strewing a little powdered chalk on the surface, the mo- 

 tions of which makes that of the water plainly visible, as 

 shown in the figure. 



15. Manner in which the young sponges are dissemi- 

 nated. In all parts of creation, whether in the vegetable 

 or animal kingdoms, there is provided effectual means for 

 the dissemination of the species. (For an account of the 

 dissemination of the seeds of plants, see the author's Intro- 

 duction to Botany.) For the distribution of the sponges, 

 the method provided is singularly curious and interesting, 

 and at the same time displays, in a most striking manner, 

 the care which the Creator has taken to perpetuate his 

 most humble works. 



16. On examining certain parts of the sponge, which, 

 when living and wet, are nearly transparent, there is 

 found a multitude of yellow, opaque spots, visible to the 

 naked eye. These, when examined with a microscope, 



Whence comes the water which is poured forth from these apertures ? 

 How does the sponge obtain its nourishment? By what means is it 

 supposed the current through the apertures are produced? How are 

 the currents made Apparent ? In what manner are the voung sponges 

 distributed? 



