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BULLETIN OF THE BUREAU OF FISHERIES 
for surface views, while many were embedded in paraffin, M. P. 54°, sectioned, and 
stained with Mayer’s hematoxylin and eosin. A nonfertilized egg sections like 
hyaline cartilage, and fry with the yolk still unabsorbed, that were fixed in formalin, 
sectioned well. However, only a very small precentage of good sections of the cleav- 
age stages were obtained. Those obtained nevertheless add much to the picture of 
the cleavage process. 
PERIOD OF INCUBATION 
The eggs in the Meehan jars hatched in 21 days. This is probably a little longer 
than the average time for the following reasons : About 5 per cent hatched at the end 
of 12 days, after which a period of cold weather delayed both eggs and fry for about a 
week. Then all hatched in two or three days. Cold weather is common at Ithaca 
even in May, so that probably 18 to 20 days is the normal period. Reighard (1915) 
gives 8 millimeters as the length of the newly hatched fry, but mine exceeded this 
by a millimeter or two, due, perhaps, to delayed hatching. The mean temperature 
of the water over the whole period was 50.5° F. 
CLEAVAGE STAGES 
One-celled stage. — Two and one-half hours. (Figs. 1 and 2.) Samples taken 
two and one-half hours after fertilization are still in the one-celled stage. The shell 
must be removed carefully with dissecting needles. This done, the germinal disk 
appears white and covers about half of the top of the egg, extending down the sides 
about 45° from the pole. The contour of the egg is still that of a sphere, and the 
protoplasmic portion is but one-half millimeter thick at the pole and thins out laterally. 
Pseudopodialike branching, processes of the disk extend down into the central region 
of the yolk. Clear droplets (oil?), twice the diameter of the yolk spheres, are found 
in the protoplasm, especially near its upper surface. Yolk spheres are sparsely but 
rather evenly scattered throughout the disk. These evidently are contributed from 
the densely packed yolk mass on which the disk rests. 
Four-celled stage. — Six hours. (Fig. 3.) At the end of four hours the germinal 
disk contracts and arches up as a conspicuous white dome, leaving distinct shoulders 
to the egg when seen from the side. By six hours this dome-shaped disk is crossed 
by the first two cleavage furrows placed at right angles. These furrows extend 
one-third to one-half the distance through the disk, and sections show the continued 
wall below each one passing on to the yolk. The nuclei are centrally located in the 
cells, which are quite sharply demarked from the yolk laterally as well as below, as 
seen in sections. No cytoplasmic extensions of the disk were observed beyond the 
one-celled stage. 
No observations were made upon the eight-celled stage. 
Eighteen-celled stage. — Eight hours. (Fig. 4.) The cell cluster is sharply out- 
lined, the cells being of nearly equal size. Cleavage planes are irregularly radial, 
resulting in an outer ring of about 11 cells surrounding the remainder, which are 
irregularly placed centrally. The outer cells are slightly larger. 
Thirty-six celled stage. — Ten and one-half hours. (Fig. 5.) The centrally 
placed cells show by their relatively smaller size the more active cleavage. Up to 
this time the general contour of the egg is as in the four-celled stage — namely, a 
dome-shaped blastodisc surmounting the spherical yolk mass. 
