176 FUNCTIONS AND INSTINCTS. 



Amongst plants, as Mr. W. S. Mac Leay has, I 

 think, remarked, sponges present some analogy 

 to the puff-balls. 1 



5. A. fifth Order of polypes, worthy of atten- 

 tion, is that to which the red coral belongs, in 

 these the animal instead of being covered, or in 

 any way sheltered by its polypary, invests it 

 completely, so as to form a kind of bark over 

 every part of it ; on this account the name has 

 been changed by writers on these animals, and it 

 is denominated their axis, since upon it they are, 

 as it were, suspended, and run their prescribed 

 race. This axis consists of a much more rigid, 

 solid and lapidose substance, than the polypary 

 of the really sheathed polypes, presenting when 

 polished the smooth substance and lustre of 

 marble, without any appearance of pores or other 

 orifices when broken it exhibits the same kind 

 of fracture as a stick of red sealing-wax ; this 

 description refers particularly to the red coral, 2 

 for in some other genera belonging to the Order 

 the axis is jointed, 3 and in others, very flexible. 4 

 The sheathed corallines appear in some sort, to 

 be analogues of those animals whose bodies are 

 covered and defended by an external crust or 

 shell, like the Testaceous Molluscans, the Crusta- 

 ceans and the Insects ; while the tribe in question, 



Lycoperdon. * Corallium. 



Isis, &c. 4 Antipathes, Gorgonia. 



