160 



giving rise to cells some of which are added ou to notochord others 

 to nerve tube, others to muscle tissue and so on. This is the 

 still active remains of the "secondary centre of growth" and itself is 

 neither ectoderm, mesoderm, or endoderm, it is simply a post-gastrsea 

 proliferating centre adding new material on to previously formed tis- 

 sues. It dates from an altogether post-gastrula period. 



Half the apparent inconsistencies which are said to occur in the 

 development of the various organs from the germinal layers are not 

 inconsistencies really, but are misconceptions due to the failure to 



- Bl 



r- Bl 



Fig. 6 Rana temporaria. The sable was inserted a little to one side of the mid 

 ventral line. During the closure of the ventral part of the blastopore, the sable is car- 

 ried up on to the side, so that on the appearance of the anus (reopening of the ventral 

 part of blastopore?) it is seen anterior and dorsal to the anus. 



appreciate the parts of the embryonic development which represent 

 the primary radial organism of the gastraea (or ccelenterate) epoch, 

 and the parts which are post-gastrsea or post coelenterate. To the 

 tissues produced by the primary centre alone should the terms ecto- 

 derm, endoderm, mesoderm be applied strictly. At least that is what 

 seems to me to be the logical outcome of the "gastra:;a" theory. 



Possibly, if, instead of calling my centres primary and secondary 

 areas of cell activity, I had in my papers ten years ago named them 

 "protogenetic" and "deuterogenetic" areas, my point njight have been 

 made more clear. 



