Conclusion 63 



expanded indefinitely without altogether losing their utility, so 

 such organs must be repeated and not expanded when the great 

 growth in length occurs. Hence it is not necessary to regard 

 metamerism as in itself indicating homology. 



The object of this short course of lectures has been to show 

 what the real relation of the main axis of the body of a Chordate 



V' 



is to the plane of the gastrula or coelenterate mouth, and to 

 indicate that it is probably quite different to that of the Annelid, 

 Arthropodan and Molluscan groups. Such a conclusion if correct 

 is quite destructive to the hypothesis of His, Semper, Dohrn, 

 Patten, Gaskell and others who would derive chordates from 

 various highly organised invertebrate groups. It agrees with 

 the views of Sedgwick, van Beneden and Hubrecht in seeking the 

 origin of chordates as far back as the Coelenterata or their 

 immediate descendants, but is equally destructive of the view that 

 the main axis of the chordate body is parallel with the plane of 

 the coelenterate mouth on the contrary it shows it to be at 

 right angles thereto. 



