NOTE ON THE DEVELOPMENT OF AMPHIBIANS. 305 
Triton corresponds with the stage of Amblystoma represented 
in figs. 12 e to 16 e. From this stage onward my series of the 
embryos of the two genera run about parallel, and a great 
similarity continues to exist throughout all the stages which I 
have examined. 
The development of the hypophysis and mouth in the Frog 
differs in a marked manner from the development of the same 
organs in Amblystoma and Triton. The same fundamental 
principles seem to obtain in both methods of development, but 
the difference is apparently due to a different proportional rate 
of growth of the parts adjacent to each other. The development 
of these parts in the Frog is illustrated in figs. 19 — 23. These 
sections are sagittal, or nearly sagittal, and all meet the 
median vertical plane in the centre of the mouth-fusion. In 
fig. 19, between the lip of the anterior medullary fold (. A . F.) 
and the mouth-fusion, lies the epiblast which is to form the 
hypophysis. In this embryo the cranial flexure is not yet 
complete, and the alimentary cavity extends forward beyond 
the anterior fold. The rudiment of the hypophysis lies there- 
fore immediately exterior to the anterior fold. In a somewhat 
older embryo (fig. 20) the brain is enclosed, and has increased 
so much in size that it projects forward anterior to the mouth- 
fusion ( M .). The increase of the cranial flexure has caused a 
change in the position of the anterior fold. In fig. 19 the 
anterior fold occupies a vertical position, and in fig. 20 it 
occupies a horizontal position (A. F.), forming in both cases 
the morphologically anterior wall of the brain. In embryos 
slightly younger than the one represented by fig. 20 serial 
sections show that the dorsal linear opening of the central 
nervous system extends as far as the horizontal anterior fold 
to about the point indicated by o. g. in fig. 20. When this 
opening becomes closed by the dorsal median fusion of the 
lateral walls, the line of fusion remains marked by the accumu- 
lated mass of cpidermoidal pigment. This pigmented line is 
cut at o.g. in fig. 20, very near the end which indicates the 
boundary of the anterior fold. It may be seen from the 
figures that the change of position of the anterior fold is 
