CHAPTER XXV. 



POLYZOA AND TUNICATA. 



We speak of the " scale of animal life," as if species rose 

 above species in a perfectly regular linear series, as to 

 their development in organisation, like the steps of a 

 ladder, beginning from the lowest, simplest forms of life, 

 and proceeding step by step, without any interruption, 

 till we arrive at the highest, Man, " who was made after 

 the image of God." This is, perhaps, the common notion 

 among those who have ever attempted to consider the 

 matter philosophically, — to contemplate Creation as a 

 whole, a system, a plan. And the notion is aided by our 

 systematic books. We are compelled, by the very nature 

 of a book, to treat of creatures in this linear manner ; we 

 cannot do otherwise : we must begin with something, 

 then go on to something else, and so proceed till we leave 

 off. Nobody has yet invented a book in which the pages 

 shall run on in parallel or complex series, instead of suc- 

 cessive ; nor would it be possible to read it otherwise 

 than successively, if it could be so written. 



However, there is much in nature to confirm the ccn> 

 men notion. Linear series we find everywhere. Proofs 

 may be found in these very pages ; we have treated of 



