CHAPTER 1. 



Stomodaeum and medullary tube. 



Phylogeny, the study of the evolution of life on earth, 

 has lost the universal veneration paid to it by a former 

 generation of zoologists. As a guiding thread in systematic 

 studies on restricted groups it still may do service; but the 

 general discouragement evoked by so numerous vain attempts 

 to trace the relations of the main branches of the genealo- 

 gical tree of the animal kingdom has diverted attention from 

 the great work of the reconstruction of this tree to other 

 problems and other paths of science, neglected until now. 

 How much interest did a theory on the origin of Verte- 

 brates awake some thirty or forty years ago. How little, 

 I fear, will it do in our materialistic days! New and vain 

 speculations on things we can never know, new hypotheses 

 based on a hypothesis: the theory of evolution. What is 

 their value? Give us facts! 



It is to encounter these objections that I gave this book 

 a sub-title which, I hope, will need no further elucidation. 

 It is equally as a plea pro domo — I nearly would have said: 

 as an excuse for my boldness to treat of such a subject — 

 that 1 placed the first quotation under the title, though, as 

 a complement, I added the second under it. And further, 

 may the theory to be exposed here speak for itself and 



