344 HORACE W, STUNK ARD 



ii 



X 



Figs. 1 to 7 and 12 to 14, camera-lucida drawings of Amblystoma embryos, 

 showing successive stages of development, the so-called primary neuromeres, 

 and the neuromeres of later stages. 



Fig. 1 Early stage in the formation of the neural folds, showing the anterior 

 thickening. 



Fig. 2 Embryo showing neural groove, the lobulations along the neural folds, 

 and transverse grooves of the neural plate. 



Fig. 3 Embryo with no evidence of segmentation in the neural folds and 

 regular transverse grooves of the neural plate. 



Fig. 4 Embryo showing irregular character of the divisions of the neural 

 folds and neural plate. 



Fig. 5 Embryo showing expanded anterior part of the neural plate, with 

 irregular divisions of the neural folds and neural plate. 



Fig. 6 Embryo elongated, with partial fusion of the neural crests. 



Fig. 7 Complete fusion of neural crests and appearance of the brain vesicles. 



