PREFACE. 



xvu 



to place the work in the hands of the students of my oavii classes, I need 

 not apologise for adding here further details of the classification which I 

 find it most convenient to adopt in teaching. I have arranged the chief 

 phyla first of all in the form of a genealogical tree, and secondly in a 

 series exhibiting their subdivisions into classes, etc. This classification is 

 of course to a large extent only a modification and adaptation of systems 

 already put forward by other naturalists. 



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Grade II. CCELOMATA. 



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Grade I. CCELENTERA. 



Grade II. ENTEROZOA. 



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Grade I. PLASTIDOZOA. 



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