JOURNAL OF MICROSCOPICAL SCIENCE. 
EXPLANATION OF PLATE X, 
Illustrating Mr. F. M. Balfour’s paper on the Early Stages 
in the Development of Vertebrates, 
Complete List of References, 
sg. Segmentation cavity. 
al, Cavity of alimentary canal. 
ep. Epiblast. 
Ll. Lower layer cells. 
m. Mesoblast, 
hy. Hypoblast. 
z. Point where epiblast and hypoblast are continuous at the mouth of 
the alimentary involution. This point is always situated at the tail 
end of the embryo. 
yk. Yolk. 
zc. Neural canal. 
ch. Notochord. 
m. Nuclei of yolk of Selachian egg. 
J. Formative cells. 
é/. Blastoderm. 
em. Embryo. 
Epiblast is coloured yellow, mesoblast red, and hypoblast green. The 
lower layer cells before their separation into hypoblast and mesoblast are 
also coloured green. 
Al, All, A 111.—Diagrammatic sections of Amphioxus in its early stages 
(founded upon Kowalevsky’s observations). 
BI, BM, B1u1.—Diagrammatic longitudinal sections of an hypothetical 
animal, intermediate between Amphioxus and Batrachians, in its early 
stages. 
CI, C1, c 11.—Diagrammatic longitudinal sections of Bombinator igneus 
in its early stages (founded upon Gotte’s observations). In c 11 the neural 
canal is completed, which was not the case in Bi. The epiblast in c III 
has been diagrammatically represented as a single layer. 
DI, Di, D1m.—Diagrammatic longitudinal sections of an animal, inter- 
mediate between Batrachians and Selachians, in its early stages. 
EI, Ell, E11.—Diagrammatic longitudinal sections of a Selachian in its 
early stages. 
_ B'.—Surface view of the yolk of a Selachian’s egg to show the manner 
in which it is enclosed by the Blastoderm. The yolk is represented green 
and the Blastoderm yellow. 
FI, FI, Fit.—Diagrammatic longitudinal sections of a Bird in its early 
stages. 
