474 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Fig. 52. The yolk of a recently hatched larva as a transparent object, showing the position of the peri- 
blast nuclei. 
Fig. 53. Longitudinal sagittal section through the yolk of a larva 5 nun. long. It lies beneath the 
anterior part of the liver. There are still yolk bodies present. 
Fig. 54. Longitudinal horizontal section through yolk of larva 7 mm. long. Yolk cells have dis- 
appeared. The yolk has been reduced to a granular mass surrounded by the liver, except 
at anterior margin which faces the sinus venosus. There are 11 nuclei in yolk of this larva. 
Figs. 55-59. Origin of the mesoderm and embryonic axis. Five sections through an egg of ovary (23) 
in some eggs, of which theblastopore was not yet closed. Sections are parallel to tangential 
of anterior end of embryo. The whole egg was cut into 25 sections, of which fig. 55 rep- 
resents the sixth from anterior end ; fig. 56, the eighth ; fig. 57, the tenth ; fig. 58, the 
twelfth; fig. 59, the fifteenth. Figs. 57-59 on plate xcix. 
Plate XCIX. 
Figs. 57-59. Three sections of an egg about the closing of the blastopore. See explanation of fig. 55. 
Figs. 60-63. The sixth, eighth, twelfth, and portion of the eighteenth sections of an egg cut into 33 
sections, the first of which is tangential to a point over the anterior part of the head. 
Plate C. 
Portion of a section through the posterior part of an egg cut in a plane about at right angles 
to that of the preceding egg. 
Section near the head of an embryo of the same stage, the plane at right angles to that of 
the first egg. 
The sixth section further back of the same egg. 
Sagittal section of an embryo with three proto vertebra;. 
A portion of a section to one side of 67, through Kupffer’s vesicle. 
Portion of another section from same embryo, showing position of the sex cells in the head. 
A section to one side of fig. 67 and parallel with it, to show the position of the protovertebra; 
and sex cells. 
-74. Four sections of another larva from the same ovary as figs. 67-70, but at right angles to 
those figures. The planes of the sections are indicated in 67. In fig. 71 the section passes 
through the anterior end of the notochord and through the median portion of the body. 
The lower portion of fig. 72 passes through the region just in front of the head, while the 
upper portion passes through the posterior region of the notochord. Fig. 73 passes 
through Kupffer’s vesicle. In this section the entoderm can no longer be traced over the 
whole yolk, but merges into the mesoderm. Fig. 74 passes through the caudal thickening, 
where the germinal layers are merged. (Figs. 73 and 74 are on plate ci.) 
Plate CI. 
Fig. 73. Sections through a larva at the region of Kupffer’s vesicle. For details see under fig. 71. 
Fig. 74. Section through the caudal thickening of the same larva. 
Fig. 75. Sagittal section of a newly-hatched larva reconstructed from a number of slightly oblique 
sections. 
Fig. 76. Sagittal section of an older larva about 0-45 mm. long. 
Plate CII. 
Fig. 77. Sagittal section of a larva 063 mm. long. 
Fig. 78. Sagittal section of a slightly older larva. 
Plate CIII. 
Fig. 79-108. Illustrate general changes of larva from time of hatching till shortly after birth. 
Fig. 79, 80, 81. Three views of a living larva just before hatching. 
Fig. 82. Usual appearance of the larva at hatching. 
Fig. 83. A larva shortly .after hatching, the tail and head in contact, encircling the entire yolk. 
Fig. 84. Outlines of a larva 0'8 mm. long, showing the three divisions of the original Kupffer’s vesicle. 
Reconstructed from a series of sections. 
Fig. 85, A slightly older larva; the eye has now become evident. 
Fig. 64. 
Fig. 65. 
Fig. 66. 
Fig. 67. 
Fig. 68. 
Fig. 69. 
Fig. 70. 
Figs. 71- 
