THE ORIGIN OK LIFE 



^53 



individual, and that each may experience hunger 

 when in want, or satisfaction when it is filled with 

 food, and that injuries to one part of the mass 

 may indirectly affect other parts, but that the 

 nutrition of the whole mass may be as much 

 unfelt by the individual Polyps as the processes 

 going on in our own bones are by us. So in the 

 case of a large Sponge or Foraminifer, there may 

 be some special sensation in individual cells, pseudo- 

 pods, or segments, and the general sensation may 

 be very limited, while unconscious living powers 

 pervade the whole. In this matter of aggregation 

 of animals we have thus various grades. The 

 Foraminifers and Sponges present us with the 

 simplest of all, and that which most resembles the 

 aggregation of buds in the plant. The Polyps and 

 complex Bryozoons present a higher and more 

 specialized type; and though the bilateral sym- 

 metry which obtains in the higher animals is of a 

 different nature, it still at least reminds us of that 

 multiplication of similar parts which we see in the 

 lower grades of being. It is worthy of notice here 

 that the lower animals which show aggregative ten- 

 dencies present but imperfect indications, or none 

 at all, of bilateral symmetry. , Their bodies, like 



