164 



elongation of the aperture after the manner of an Actinian mouth ; the 

 organism elongated as a whole along an axis passing vertically through 

 this aperture which became the anus. The mouth was a new opening 

 like the gill slits. 



As regards Sedgwick's theory with reference to the origin of, 

 say, Annelida, Arthropoda, and Molluscs from a gastrsea or Actinian 



B 



Fig. 8. Diagrams foi- comparison of the protogenetic and deutei'ogenetic centres 

 in Chordates and Annelids. For further explanation see the text. 



by drawing out of the mouth I have 

 nothing to urge against it — in fact 

 it is supported by much evidence. 



But as regards Vertebrates, or 

 rather the Chordates, on what does 

 Sedgwick's theory, as restated by 



Fig 9. Diagram to shew the protogenetic 

 and deuterogenetic centres and their products in 

 a chordate with a meroblastic egg and mammal. 

 In this and two preceding figures the dotted and 

 shaded area is the deuterogenetic area. 



HuBRECHT, rest? The evidence of the blastopore is entirely against 

 it. I think I have shewn reason to conclude the relation of the two 

 centres of growth as determined by experiment is against it. It rests 



