424, BASHFORD DEAN. 
the eggs hatched far more rapidly than this during the latter 
part of the present season,—in one case (May 24) within four 
days, in all cases not longer than eight. A sudden increase in 
the water temperature, as in the Lepidosteus, and, for that 
matter, doubtless as in all other fishes, hastens the rate of 
development. 
C. Segmentation.—The segmentation stages of Amia 
are readily studied in the living egg, the transparency of its 
membranes permitting the cleavages to be followed. They are, 
however, far more obscure than those of the other Ganoids, and 
impress the observer with their marked Teleostean characters. 
They are readily reduced to the plan of those of Lepidosteus ; 
and the accompanying figures (PI. 30, figs. 1—9) may be in- 
structively compared with those in the ‘ Journal of Morphology,’ 
vol. xi, pl. i, figs. 1—9. And, on the other hand, they closely 
suggest the plan of segmentation of the Teleost, e.g. that of 
Serranus.’ In the following description, accordingly, it will 
be the writer’s purpose to emphasise these more important 
comparisons, 
In general it may be said that the egg of Amia is mero- 
blastic, that its (earlier) cleavages are confined entirely to the 
germinal area, that the compact blastomeres are Teleost-like, 
and that the segmentation cavity is practically wanting. 
First Cleavage (Pl. 30, fig. 2) —In the living egg the first 
cleavage passes at once vertically through the germ area, 
causing the resulting blastomeres to be closely opposed. In 
the preserved material, however, the rim of contact (as in Pl. 30, 
fig. 3) appears somewhat rounded. At this stage the lower rim 
of the germ disc presents a more definite line of contact with 
the yolk, and the cleavage plane rounds off the corners of the 
blastomeres. In the transverse vertical section shown in 
(Pl. 31, fig. 21) are illustrated the depth and the character of 
the cleavage plane ; it has passed slightly deeper than the 
niveau of the nuclei, but leaves below it a well-marked layer 
of the germinal protoplasm; the germ disc in this region has 
1H. V. Wilson, “The Embryology of Serranus atrarius,?’ ‘ Bull. 
U.S. Fish Comm.,’ 1891, pp. 209—277, 
