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use of a relatively larger amount of stain per egg. Most of the in- 

 jury is of the nature of a burn. Id some cases no development took 

 place, the spots remaining in their original condition and position for 

 several days. In other cases the movement of the material of the 

 Randzone downwards was prevented. Development, however, continued 

 but the embryos were spina bifida forms. In other cases development 

 was normal, the blastopore closing in the usual way. In the last cases, 

 the blue spots extended into bands, just as in the case of Spelerpes 

 and Amblystoma: diagram B. The bands were of approximately equal 

 length as in Amblystoma. The closure of the blastopore of these forms, 

 takes place, then, just as described by Kopsch, who studied the cell 

 movements of the frog's egg by photographic method. This manner 

 of blastopore closure was designated convergence by Jordan, without, 

 however, any experimental proof of the correctness of his conclusions. 



My experiments afford added proof of the inapplicability of the 

 theory of concrescence to amphibian development. 



It has been shown by several investigators, that while the tail of 

 the embryo forms always at the point of closure of the blastopore, the 

 head develops at some point above the equator. In the frog this point 

 lies just a little above the equator; in the toad about half way up, 

 while in such urodeles in which this point has been determined, it lies 

 near the upper pole of the egg. Now since the material, out of which 

 the embryo is to form, lies at the equator of the egg immediately pre- 

 vious to gastrulation, moving during the latter process along the me- 

 ridians of the egg to the point of closure of the blastopore at the 

 lower pole of the egg, which point marks the tail of the embryo, it 

 follows that the embryonic (in narrow sense) material is limited to a 

 vertical half of the egg. Therefore, the material which lies on either 

 side, 90° from the meridian which coincides with the future median 

 plane of the embryo, will form only tail, while the material of the 

 equator at the median meridian itself contributes to formation of neck, 

 trunk and tail. Or, in other words, the material which lies at the 

 point where the future median plane of the embryo crosses the equator 

 is more complex, in the sense that it normally gives rise to more 

 parts of the body, than points on the equator 90° therefrom. Those 

 parts of the equator which lie at one side of the median point be- 

 come successively simpler, the further they are removed from the 

 median point. The half of the equator not involved in the formation 

 of the embryo gives rise to ventral ectoderm. 



Owing to the variation in the heighth of the head of the embryo 

 above the equator in various amphibia it follows that the Randzone 



