THE EARLY DEVELOPMENT OF AMIA. 439 
Absenceof neurenteric canal is,again, Teleostean. In this regard 
its features are notably transitional between those of Lepi- 
dosteus and the Teleost. At the closure of the blastopore, 
Pl. 82, fig. 35, there is no trace of the neural groove in the 
hinder region, the outer germ layer here fusing in a solid plug, 
merging below into the undifferentiated tissue, w; at a later 
stage, Pl. 32, fig. 88 (cf. H. V. Wilson, op. cit., pl. xeviii, 
fig. 84), the ventral lip of the blastopore has become largely 
merged with the growing tissue, w, of the tail region, and the 
conditions are markedly Teleostean. 
The inner germ layer has already been noted (p. 481) in 
its intimate relationship to the yolk mass. In PI, 82, fig. 31, 
the entoderm is clearly defined, extending forward from the rim 
of the dorsal lip to about the position of the point®*, having in 
its texture all the characters of the similar stage in gar-pike and 
sturgeon. Beyond this point, however, it merges into the 
loose layer noted on p. 431, whose periblast-like characters have 
already been indicated (p, 434). The growth in extent of the 
entoderm may befollowed in Pl. 32, figs. 31—86, 38, 39; under 
the ventral lip of the blastopore it appears for a short distance 
(fig. 35) as a separate layer, but in a later stage (fig. 39) it 
becomes merged with the yolk entoblast; under the blasto- 
pore’s dorsal lip the darm-entoblast has separated from the yolk 
region (apparently by differentiation of the cells in situ) as far 
as the point * in fig. 33, and as far as the most anterior head 
region in fig. 84; at its periphery the cells become indistin- 
guishable from those of the neighbouring yolk. The gut arises 
in a manner closely resembling that of Acipenser ; its cavity, 
narrow and deep (fig. 34) tailward, flattens out broadly in the 
head region, as is shown in the marginal limits of the parietal 
zone of PI. 30, figs. 17—20 ; its mode of formation, it should be 
noted, although of clearly marked Ganoidean character, 
diverges, nevertheless, toward the plan of the Teleost; it has 
not, however, acquired the yolk-apposed characters of the 
latter. The notochord arises as in the sturgeon or gar-pike 
(Pl. 32, fig. 38): it separates directly (i.e. delaminates) from 
the entoderm; in the region of the hind brain, as seen in 
