44.0 BASHFORD DIAN. 
Pl. 32, fig. 36, it is undifferentiated from the loosely associated 
cells of the lower layer. 
The mesoblast is notably peristomal (Pl. 32, figs. 38— 
36, 88, 39); it is hardly to be distingushed in the blastopore’s 
ventral lip (cf. figs. 35, 39): its appearance is first noted in the 
gastrula of fig. 33. In its early growth it extends forward as 
a wide and flattened cell mass, thinning distally, and becoming 
confluent with the inner germ layer. As in the Teleosts, gas- 
tral mesoderm is absent, and the division of the middle layer 
into its somatic and splanchnic layers is not apparent until 
comparatively a late stage ‘of development. A contrast with 
the conditions of the mesoblast in Acipenser and gar-pike may 
be made by reference to the table in Dean, op. cit., p. 47. 
TII. Concivustons. 
The early development of Amia, as outlined in the foregoing 
paper, must certainly be regarded as furnishing abundant evi- 
dence of intermediate characters. To the Ganoids on the one 
hand, and the Teleosts on the other, these ontogenetic near- 
nesses become, accordingly, of the greatest interest, since they 
confirm the results of the structural study of recent and fossil 
forms upon the Amioid descent of Teleosts. 
A comparison of the developmental characters of Amia with 
those of the gar-pike and sturgeon need be but briefly reviewed. 
Its type of development is in many ways curiously Lepidos- 
teoid, as in meroblastic segmentation, relations of blastoderm 
to yolk, flattened segmentation cavity, late gastrulation, early 
neuron, and absence of neurenteric canal. It certainly re- 
sembles that of the sturgeon in some of its advancing cha- 
racters, as in the mode of closure of the blastopore, decreased 
prominence of its ventral lip, and in the embryo’s sagitally 
accented growth. From either of these older Ganoids the 
developmental type of Amia is nevertheless sufficiently different 
to warrant any definite conclusions as to its descent; one 
might, the present writer believes, safely infer that, like that of 
the sturgeon, it is in general Lepidosteoid. 
But the early development of Amia is clearly to be recognised 
