CHAPTER XXVI. 



OF THE CLASS OF PORIFERA. 



1137. THE lowest of the classes usually comprehended under 

 the Radiated type, is one whose claim to a place in the Animal 

 Kingdom must be regarded as very doubtful. Not only is the 

 radiated disposition of parts altogether wanting, but even that 

 definiteness of form is absent, which so peculiarly distinguishes 

 the higher groups of Animals from the members of the Vegetable 

 Kingdom. The absence of charac- 

 teristic structure does not extend to 



external form alone ; it is equally 

 remarkable in the internal arrange- 

 ment of the parts, of which these beings 

 are composed. There is no stomach 

 or digestive cavity for the reception of 



,. FIG. 628. SPONGE. 



food, no nervous system or organs for 



sensation or locomotion, and nothing beyond the very simplest 

 apparatus for reproduction. In the vital actions performed by 

 these beings, there is nothing distinctly characteristic of an 

 Animal nature. No movements can be observed, either in the 

 whole structure, or in portions of it ; neither is there any indica- 

 tion of the possession of sensibility. In fact, the only obvious 

 vital action which can be observed in their ordinary state, is a 

 movement of fluid through their channels ; and this does not 

 differ, except in rapidity, from what may be seen in Plants. 



1138. There can be little question, then, that if the Class 

 PORIFERA, consisting of the Sponges and their allies, is to be 

 ranked in the Animal creation, the lowest place in the scale is 

 justly assigned to it; since the beings which it contains exhibit 

 so few indications of any but organic life, that it has been, 

 and perhaps still may be, doubted, whether they should not 



