THE EARLY DEVELOPMENT OF AMIA. A29 
D. Blastula.—A typical stage of the blastula is figured in 
vertical section in Pl. 31, fig. 29, and a somewhat later stage 
in surface view in Pl. 80, fig. 10, and in section in Pl. 31, 
fig. 30. The latter, contrasted with the sections of figs. 28 
and 29, indicates clearly the downgrowth and the greater 
depth of the blastoderm ; its cells have greatly increased in 
number, and build a dome-shaped cell cap of nearly twice 
the thickness of that of fig. 28; its cells are small, spherical, 
and of uniform size; those of the surface layer, however, 
have compacted into a firm cell stratum, e’, and those in the 
lowermost part of the blastoderm are slightly larger, yolk- 
laden. In this region the space between the loosely associated 
cells (sc.) is evidently to be compared with that (sc.) of the 
former figures. The segmentation cavity will be noted to extend 
irregularly between the blastomeres as far as the outermost 
cell stratum. Its floor is flattened, and bears a tier or more 
of irregular, upwardly projecting yolk-cells, and below them 
a merocyte-bearing zone of yolk. 
The conditions of the blastula of Amia present interesting 
resemblances to those of Lepidosteus, and especially to those 
of the Teleosts. 
The resemblances to the Teleostean blastula (e.g. cf. H. 
V. Wilson, op. cit, fig. 27) include—the lenticular shape of 
the blastoderm, the general uniformity of its elements, the 
differentiation of the outermost cell stratum, the apparent re- 
lations of the yolk nuclei to mode of growth of the blastoderm. 
In the latter regard it cannot be doubted that the closest func- 
tional kinships to the periblast are present; cell increments 
are being constantly made in the plane of the base of the 
blastoderm through the agency of a layer of nucleated elements 
derived from the yolk region. 
E. Gastrula.—Typical conditions of the gastrula have 
been figured in surface views in Pl. 30, figs. 12, 13; an early 
stage in fig. 11, and two of the closing stages in figs. 14, 15. 
Like the blastula, it proves of considerable interest in com- 
parison with the conditions of the older Ganoids on the one 
hand, and of the Teleosts on the other. 
VOL. 38, PART 4,—NEW SER. GG 
