DEVELOPMENT OP SPELERPES BILINEATUS 241 



18. The primary egg axis becomes the anterior posterior axis 

 of the embryo, 



19. The amphibian egg may be divided by a vertical plane 

 into halves, one of which is dorsal and the other ventral. This 

 statement is true for the surface of the egg, although the process 

 of gastrulation, may render it less accurate if applied to the inte- 

 rior of the egg. This explains the observed absence of posterior 

 half embryos. 



20. Marks made at the equator of the egg spread into bands 

 over the ventral half of the egg during gastrulation. These bands 

 are approximately meridional. They converge at the blastopore. 



21. The dorsal lip of Spelerpes is often nearly stationary, 

 although it may advance as much as 35°. 



22. The blastopore often shifts to one side or the other of its 

 original position. 



23. A temperature of 5° C. has no effect on the eggs of Speler- 

 pes beyond slowing the rate of development. 



24. Salt solutions fail to produce more than one form of spina 

 bifida larvae, namely those with divergent posterior neural folds. 

 The anterior two-thirds of the embryo is always intact, 



25. The photographic studies of Kopsch, the pricking experi- 

 ments of Eng and others and my own work on Spelerpes show 

 that the posterior part (in various amounts, according to the 

 species) of the amphibian embryo is formed by the convergent 

 distribution of the embryonic material, which as gastrulation 

 begins lies in a half ring about the equator, over the lower hemi- 

 sphere of the egg. There is no concrescence except in a very 

 limited region about the blastopore, after it has become slit-like. 



