THE EARLY DEVELOPMENT OF AMIA. 425 
become slightly deeper. The first cleavage was observed in 
several instances to divide the germ disc into blastomeres of 
unequal size ; this abnormality, however, as in Lepidosteus,' 
Teleosts,? as well as in other Chordates, was found to in no way 
influence the subsequent developmental stages. 
The writer, it might be here noted, has taken especial care to 
verify his observations on the meroblastic character of the 
cleavages of Amia. During the first few cleavages several 
hundred living eggs were examined with a view of determining 
holoblastic variations. These, however, did not occur, nor 
were there found even by the most favorable means of 
illumination, traces of what might be construed as surface 
furrows traversing the yolk region of the egg. In no case did 
a marginal cleavage pass below the rim of the germinal disc.® 
Second Cleavage (Pl. 30, fig. 3) passes in a vertical plane 
at right angles to the first cleavage. This it closely resembles 
in depth and marginal limits; and in this stage the nuclei 
retain the same niveau with similar relations to the yolk. 
Immediately below animal pole the blastomeres slightly 
separate, giving rise to the beginnings of the segmentation 
cavity. In an examination of a number of eggs at this stage 
but very few (2 per cent.) variations were observed, the second 
plane in these cases intersecting the first at an angle of about 
70°. Polflucht was in no instance noteworthy. 
Third Cleavage (Pl. 30, fig. 4).—This cleavage plane is 
RTT 
Fic, 5.—Variations in the stage of third cleavage. 
again vertical, and, as in Lepidosteus and Teleosts, at right 
angles to the preceding plane (i. e. parallel to the first cleavage). 
In this stage variations were found to be common (20 per cent.), 
1 Dean, op. cit., p. 16. 
2 Ryder (cod), H. V. Wilson (Serranus), Whitman, and others. 
3 Cf, the somewhat different view of Fiilleborn, op. cit., p. 1061. 
