oo PROCEEDINGS OF THE NATIONAL MUSEUM, 139 
ing the net from the wharf as far as it would reach and drawing it in 
again. They were first noticed April 18, 1889, when eight eggs were 
found. They soon became very abundant and remained so until July. 
There is but a small water space in the egg membrane, and the germ 
lies at the end of the longer axis of the egg just beneath the micropyle. 
The physiological axis of the egg, therefore, corresponds to its longer 
structural axis. 
The fertilization and the earliest stages in the segmentation were not 
observed in any of the pelagic eggs. All the eggs found had evidently 
been deposited in the evening. The segmentation progresses rapidly, 
being completed in about eleven hours. At this time the blastoderm 
rests on the periblast only on its outer margins. The periblast dips 
deeply into the yolk, leaving a large, concayvo-convex-shaped seg- 
mentation cavity, to the bottom of which cells from the blastoderm 
sometimes fall (Fig. 1). This is probably the stage termed the ‘blas- 
tula” by Ryder. Some time after the infolding of the margin of the 
blastoderm the segmentation cavity is almost entirely obliterated by 
the ingrowing cells. The inner margin of the embryonic shield reaches 
beyond the middle of the blastoderm, and by the time the blastoderm 
covers half the yolk the embryo extends entirely across the ectodermic 
end of the yolk (Figs 2 and 3). The anterior and posterior margins of 
the embryonic ring extend evenly over the yolk and the blastopore 
closes at the entodermic pole. 
M. Kowalewski concluded, from several preserved oval eggs, that the 
posterior margin advanced but little, while the anterior edge moves 
over the greater portion of the egg, the blastopore closing near the 
ectodermic pole. It would seeem that such a closing of the blastopore 
would be somewhat precipitous after the embryonic ring had passed the 
entodermic pole of the egg. He has superimposed the stages in his 
possession in a single figure. The latest stage—one about correspond- 
ing to astage intermediate between my Figs. 9 and 10—he has drawn 
upside down, which would bring the closing of the blastopore about 
where the auditory capsule of my Fig. 10 comes to lie. His first two 
stages are either pathological (which would account for the eccentric 
positions of the blastoderm), or the blastodise in the species studied by 
him is normally placed to one side of the exact mechanical pole of the 
ege. 
In the eggs observed by me the tip of the head soon comes to a state 
of rest while the posterior growing end of the embryo advances over 
the yolk. 
The blastopore closes in about eighteen hours. Kupffer’s vesicle dis- 
appears in about twenty-four hours. At the closing of the blastopore 
the embryo extends somewhat more than half way around the yolk. 
The embryo hatches in about forty-eight hours and measures 1.79 
millimeters. The tail is sharply bent down over the yolk, making 
almost a right angle with the axis of the body, so that the vigorous 
