12 ON CLASSIFICATION. 



tribe of beings presenting an advance upon the preceding, and 

 merging insensibly into that which follows it ? A very slight 

 investigation of this matter will convince us of the contrary. Each 

 group, in fact, will be found to present points of relationship with 

 several others, into all of which it passes by connecting species ; as 

 a circle would, at different points of its circumference, touch others 

 placed around it. This, however, will be best illustrated as we 

 proceed. 



CHAPTER IT. 



ON SPONGES. 



Porifera,) Grant Amorphozoa (Blainville). 



(1 5.) The great circles to which we may compare the animal and 

 vegetable kingdom, like the smaller circles to which allusion was 

 made at the close of the last chapter, touch each other ; or, in 

 other words, there are certain forms of organization so closely 

 allied to both, that it is difficult to say precisely in which they 

 ought to be included. Such are the sponges, which, although by 

 common consent admitted into the animal series, will be found to 

 be excluded, by almost every point of their structure, from all the 

 definitions of an animal hitherto devised. What is an animal ? 

 How are we to distinguish it as contrasted with a mineral or a 

 vegetable ? The concise axiom of Linnaeus upon this subject is 

 well known, " Stones grow ; vegetables grow and live ; animals 

 grow, live, and feel." The capability of feeling, therefore, 

 formed, in the opinion of Linnaeus, the great characteristic sepa- 

 rating the animal from the vegetable kingdom ; yet, in the class 

 before us, no indication of sensation has been witnessed ; contact, 

 however rude, excites no movement or contraction which might 

 indicate its being perceived ; no torture has ever elicited from them 

 an intimation of suffering ; they have been pinched with forceps, 

 lacerated in all directions, bored with hot irons, and attacked with 

 the most energetic chemical stimuli, without shrinking or exhibit- 

 ing the remotest appearance of sensibility. On the other hand, 

 in the vegetable world we have plants which apparently feel in 



