22 



Growth in length of the Vertebrate Embryo 



which had been operated upon in the same way as B. Here the 

 operation scar certainly appears to have moved towards the 

 mid-dorsal line. But if we come to examine sections, we 

 find that the mid-dorsal and dorso-lateral parts of the embryo 

 are quite unaffected. It is the part of the embryo ventral to 

 that which will be derived from the protovertebrae which is 

 inj ured. 



B 



Fig. 12 after Kopsch. Egg of trout. Diagram to show the 

 result of injury to the rim of the blastoderm. 



A blastoderm; op injury; B the embryo some days later; C another specimen. 



The notochord, neural tube, and even the protovertebrae are 

 normally developed, but a little of the tissue beyond that is to 

 say, ventral to this point is lost. This means that it is the side 

 or lateral body wall of the future animal which will show a 

 deficiency, and this is only what one would expect upon the non- 

 concrescence theory. 



An injury made in the mid-dorsal line completely prevents 

 any addition to the mid-dorsal region of the embryo. If the 

 embryo were formed by concrescence this would not be so. 



