THE EARLY DEVELOPMENT OF AMIA. 4.4] 
as of an advancing type. It bridges over in many and important 
characters the gap which has always been pointed out as 
separating the Ganoids and the Teleosts. Its abbreviated 
development indicates, in short, the very stages which are most 
abbreviated in the cenogenesis of the latter group. Its mero- 
blastic mode of cleavage is decidedly Teleostean, especially in 
the relations of its segmentation cavity and yolk nuclei, 
although in these regards it also closely resembles Lepidosteus. 
Its transitional characters are most clearly marked during 
gastrulation, and during the early growth of the embryo. 
These Teleostean features might, in conclusion, he briefly 
summarised. 
Small area of blastoderm at the beginning of invagination 
(?). Flattened segmentation cavity. Early relations of inner 
germ layer of dorsal lip with periblast-like conditions of the 
yolk cells; coelenteron is then practically confluent with the 
segmentation cavity. General thinness of the down-growing 
blastoderm, whose Randwulst corresponds to the germ-ring ; 
close apposition of blastoderm to yolk mass. Early appearance 
of the embryo ; and in general early differentiation of the germ 
layers of the blastopore’s dorsal lip, attended by a corresponding 
lack of differentiation of the ventral lip. The mode of the 
closure of the blastopore; the presence of Kupffer’s vesicle 
and the absence of neurenteric canal. The early growth of the 
neuron as an insunken tract thickest in the sagittal plane. 
The early prominence of the brain mass. The evanescent 
medullary groove ; the solid character of the early neuron, and 
its secondary mode of acquiring a neural canal. The peristomal 
mode of origin of the mesoblast ; its late differentiation; the 
absence of gastral mesoblast. The early mode of establish- 
ment of the embryo’s outward form. 
