648 Chas. B. Wilson, Experiments on the Early Development etc. 



Figs. 17 — 20 are median longitudinal sections of Amblystoma embryos, 



showing method of closure of the blastopore, and the relation between the 



withdrawal of the yolk plug and the shape of the archenteron. 



Fig. 17. Median section of an egg developed 91 hrs. in a 0.6 o/q salt solution, 

 showing very large, free yolk plug and temporary anus just beneath the 

 dorsal lip of the blastopore. 



Fig. 18. Similar section of an egg developed 108 hrs. in a 0.6 o/q salt solution, 

 showing elongation of embryo, uniform depth of the archenteron and en- 

 largement of dorsal lip of blastopore. 



Fig. 19. Similar section after 140 hrs. development, showing change in shape 

 of Archenteron due to partial withdrawal of yolk plug. 



Fig. 20. Similar section after 6 days development in 0.5% solution, showing 

 further change in shape of Archenteron, almost complete withdrawal of 

 yolk plug, and formation of vertebral somites and brain. 



Fig. 21. Similar section from normal embryo at about the same period in its 

 development showing comparative shape of Archenteron. 



