POLYZOA AND TUNICATA. 
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CHAPTER XXY. 
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 stop, 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 arc 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 com- 
mon notion. Linear series we find everywhere. Proofs 
may be found in these very pages ; we have treated of 
