SPONGIDA. 6/ 



satisfied of the animal nature of sponges, although they once were 

 thought to represent the lowest and most obscure grade of animal 

 existence, and that so close to the confines of the vegetable world, 

 that it was considered difficult in some species to determine whether 

 they were on the one side or the other. " Several of them, however," 

 says Mr. Gosse, " if viewed with a lens under water while in a living 

 state, display vigorous currents constantly pouring forth from certain 

 orifices ; and we necessarily infer that the water thus ejected must be 

 constantly taken in through some other channel. On tearing the 

 mass open, we see that the whole substance is perforated 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." 



The physiological function of the tubes and orifices which 

 present themselves on all parts of the sponge has been interpreted in 

 various ways. Ellis, writing in 1765, supposes that they were the 

 orifices of the cells occupied by the polypes. In 1816 Lamarck still 

 advocated this opinion ; and even now we find the observer whose 

 notes M. Fredol has edited with so much judgment asserting that 

 " the inhabitants of the sponge are a species of fleeting, transparent, 

 gelatinous tubes, susceptible of extension and contraction ; young 

 polypes, as we may call them, without consistence, without cilia ; 

 incipient polypes, in short, of very simple but sufficient organisation. 

 The animalcule of the sponge is a stomach, without arms, very 

 simple, very elementary — in short, an animal all stomach ! " 



This mode of considering the sponge is not conformable to the 

 views of the leaders of modern science. Professor Milne-Edwards, 

 for instance, in place of seeing in the sponge a collection of united 

 beings, forming as it were a colony, considers each to be an isolated 

 being, a unique individual. The innumerable canals by which the 

 sponge is traversed, according to that author, are at once its digestive 

 organs and breathing pores. The vibratile cilia are necessary to the 

 renewed aeration of the water required as a respiratory iluid in the 

 interior canals of the sponge. The currents in these channels have 

 one constant direction. The water penetrates the sponge by nu- 

 merous orifices of minute dimensions and irregular disposition ; it 

 traverses channels in the body of the mass, and finally makes its 

 escape by special openings. According to this view, the channels of 

 the sponge perform the two functions of digestion and respiration. 

 The rapid currents of aerated water which traverse them lead into 



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