SPONGES. 147 



ever, scarcely worth while, at the present day, 

 to change a name so generally received as that 

 of Zoophytes, and the application of which is 

 not likely to lead to any misunderstanding. 



§ 2. Porifera, or Sponges. 



Among Zoophytes, the lowest station in the 

 scale of organization is occupied by the tribes of 

 P or if era, the name given by Dr. Grant to the 

 animals which form the various species of sponge, 

 and which are met with in such multitudes on 

 every rocky coast of the ocean, from the shores 

 of Greenland to those of Australia. Sponges 

 grow to a larger size within the tropics, and are 

 found to be more diminutive, and of a firmer 

 texture, as we approach the Polar circles. Dr. 

 Grant observes* that they are met with equally 

 in places covered perpetually by the sea, as in 

 those which are left dry at every recess of the 

 tide. They adhere to, and spread over the sur- 

 face of rocks and marine animals, to which they 

 are so firmly attached that they cannot be re- 

 moved without lacerating and injuring their 

 bodies. " Although they thrive best," he farther 

 remarks, " in the sheltered cavities of rocks, 

 they come to maturity in situations exposed to 



* Edinburgh Philosophical Journal, vol. xiii. p. 94. 



