NOTE ON THE DEVELOPMENT OP AMPHIBIANS. 297 
mately related to each other in the process of their development. 
Much of what I have written will have been readily inferred 
by embryologists, though the embryology of the genus on 
which most of my work is based has not hitherto been worked 
out. But as some of my conclusions are different from those 
previously expressed, I have thought best to give in detail a 
description of the facts that the reader may thereby test my 
conclusions. 
The first differentiation of the central nervous system of 
Amblystoma appears as figured in the sagittal and transverse 
sections (figs. 1, 2 a, G a). The transverse section is cut through 
the middle dorsal region. By the thickening of the dorsal 
epiblast there are formed two broad epiblastic plates (M.P.), 
connected with each other on the median line by a thinner 
portion of epiblast. A slight longitudinal groove ( G .) is formed 
by the sinking inward of this thinner median portion of epi- 
blast. Directly underneath this groove there is a longitudinal 
fold in the hypoblast, which causes a conspicuous median 
groove in the roof of the alimentary tract. The dorsal part 
of this hypoblastic fold touches the epiblast along the median 
line; and the part adjacent to the epiblast is the part which 
later forms the notochord. On each side of the hypoblastic 
fold, and apparently fused with it, lie the two layers of the 
mesoblast [So., Sp.). An examination of all my sections shows 
that the condition of the mesoblast at this point is the same in 
Amblystoma as Her twig discovered it to be in Triton. 1 
Some of my sections show a space between the two layers of 
mesoblast continuous with the archenteron. I have not found 
any trace, however, of mesoblast originating from any other 
part of the hypoblast or from the yolk. 
The sagittal section (fig. 1) passes through the epiblastic 
groove (G.) and the dorsal groove in the hypoblast, thus cutting 
only the thin median part of the epiblast aud the hypoblast. 
The sections on either side of this median section pass through 
the thicker part of the body wall, which contains also the 
1 For a statement of Hertwig’s results, see A. C. Haddon, ‘ An Introduc- 
tion to the Study of Embryology,’ 1887. 
