Eocperiments on Trout Eggs 23 



An injury inflicted at a point between that of Fig. 12 A and 

 the tail bud brings about a defect in the dorso-lateral region, 

 leaving intact the median structures, such as the notochord and 

 the floor of the neural tube. 



These experiments, to my mind, are quite conclusive against 

 the theory of concrescence or confluence in any form, but it is 

 only fair to say that this view is not held by all. 



Even Kopsch, from whose work I have taken these figures, 

 believes that his experiments indicate a certain amount of con- 

 crescence for the hinder end. He shows how, for instance, as in 

 Fig. 12 C, that there is a movement of the point of injury nearer 

 to the median line. It is true there is a change of position with 

 reference to the yolk mass, but where is there any evidence that 

 the dorsal or dorso-lateral region is affected by such an injury? 

 It is in the much distended latero-ventral region of the young 

 embryo that the injury has been made, and it is in that region of 

 the fully- formed embryo that the injury persists. So long as the 

 notochord and the floor of the neural tube are uninjured by such 

 experiments as these, so long is there a complete absence of 

 evidence for concrescence or confluence. 



Goodale stained groups of cells in the equatorial region just 

 prior to gastrulation. These groups lengthened out meridionally 

 and converged upon the blastopore. 



This showed that as deuterogenesis effected its work, the lips 

 of the blastopore progressed leaving trails behind them which 

 showed not a trace of concrescence. 



