MAEINE ZOOLOGY, 



Sub-Kingdom I. PROTOZOA. 



Class I. PORIPHORA. 



(Sponges.) 



These are the lowest grades of animal life, so 

 close to the border of the vegetable kingdom, that 

 it is difficult to determine of some species whether 

 they are on the one or the other side. To the 

 unassisted sense they seem mere lifeless masses ; 

 without organs, without feeling, without function, 

 and many of them without form, — woolly masses 

 of fibres more or less compacted, and steeped in 



Several of them, however, if viewed with a 

 lens while in a living state, under water, display 

 vigorous currents constantly pouring forth from 

 certain orifices ; and we necessarily infer that the 

 water thus ejected must be as constantly taken in 

 through some other channel. On tearing the 

 mass open, we see that the whole substance is per- 

 forated in all directions by irregular canals leading 

 into each other; of which some are slender and 

 communicate with the surface by minute but 

 numerous pores, and others are wide, and open by 

 ample orifices. Through the former the water is 

 admitted; through the latter it is ejected. 



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