VIVIPAROUS FISHES OF THE PACIFIC COAST. 
473 
Fig. 23. Horizontal section of another egg. 
Fig. 24. Section of an egg at the end of the eighth segmentation, with about 278 nuclei. 
Fig. 24a. Outline of Agassiz & Whitman’s figure of the ninth segmentation, more than 250 nuclei of 
Ctenolabrua. 
Plate XCVI. 
Fig, 25. Section, median, vertical, of another egg, from the ovary from which the egg figured in 24 was 
taken, showing a periblast nucleus and the yo.lk nucleus. 
Fig. 26. Surface view of an egg in an advanced stage of segmentation. 
Fig. 27. Median vertical section of an egg probably near the end of the ninth segmentation. 
Fig. 28. Oblique section of another egg from same ovary, plane of the section indicated in fig. 27. 
Fig. 29. Median vertical section of an egg during the eleventh segmentation (with 730 nuclei). The 
yolk nucleus has spread over the yolk and meets the layer of epiblast cells. 
Fig. 30. Oblique vertical section of another egg in about the same stage as fig. 29. 
Fig. 30a. Outline of Agassiz & Whitman’s figure, representing a section of an egg with amphiasters 
of the thirteenth segmentation, or with between 4,000 and 8,000 cells. 
Fig. 31. Diagram of an egg during the eleventh segmentation, showing the directions of the planes 
of figs. 32, 33, and 34. 
Figs. 32, 33, 34 are from an egg during the eleventh segmentation (with about 1,700 nuclei). The egg 
is cut into 21 sections; fig. 32 is the 7th section; fig. 3:3, the 10th; fig. 34, the 13th. 
Figs. 35, 36. Sections through early gastrula and blastopore. Egg contained about 3,000 nuclei ; 12th 
segmentation. Egg was cut into 17 sections, of which fig. 35 represents 10th and fig. 36 a 
portion of 11th. The sections cut through the embryonic axis obliquely. The entoderm 
is well separated from the ectoderm and contains smaller cells. The outermost layer of cells 
is continued beyond underlying layers, and nearly covers yolk nucleus: 
Plate XCVII. 
Fig. 37. The ninth section through the same egg shown in figs. 35 and 36. 
Fig. 38. A section through another gastrula of the twelfth segmentation, slightly older than the one 
figured in 37. The yolk nucleus, yk.pr, is brightly stained. It is bluntly conical, forming 
a plug in the blastopore. 
Fig. 39. A section through the blastopore of an egg from ovary 26. 
Fig. 40. A section through the blastopore of another egg from the same ovary (26). 
Figs. 41, 42. Sections from an egg during the twelfth segmentation (containing about 3,100 nuclei). 
The yolk nucleus forms .a large plug in the blastopore, and has a decided purple tinge, 
while the blastoderm cells have been colored blue by haematoxyliu. Some of the peripheral 
cells are distended and very lightly stained. Fig. 41 represents a section through the middle 
of the blastopore ; fig. 42 is a few sections removed from fig. 41. 
Fig. 43. Section of an egg shortly after the closing of the blastopore. The division between ento- 
derm and ectoderm is indicated by a heavy line. Some of the outer cells, as in fig. 41, are 
faintly stained with an alcoholic solution of fuchsine. A mass of dark granules are col- 
lected near the blastopore, and probably represent the remnant of the yolk nucleus. 
Plate XCVIII. 
Figs. 44-54 illustrate the formation and fate of the periblast. 
Fig. 44. Section through the margin of a blastoderm with about 120 cells. 
Fig. 45. Portion of a cross-section of an egg with about 220 cells; nucleus 11 /i in diameter. 
Fio-. 46. Section through margin of blastoderm of egg with about 450 cells; nucleus 9 p in diameter. 
Figs. 47, 48, 49. Three successive sections from the same egg. There are about 11 periblast nuclei in 
this egg. The nuclei are about 10 n in diameter. 
Fig. 50. The second section of the egg from which figs. 47-49 were drawn. The nuclei in this section, 
as in fig. 6, are in pairs near the margin of the blastoderm. The egg from which figs. 46-50 
are drawn contains 5 pairs of such nuclei. The fact that they are in pairs is probably due 
to the recent division of the nuclei. Paired nuclei were also found in the egg from which 
fig. 45 is taken, at end of ninth segmentation. 
Fig. 51. Section slightly inclined from the horizontal of an egg in the same stage as figs. 47-50, show- 
ing the grouping of the periblast nuclei and the relation of the periblast protoplasm (shaded) 
to the blastoderm and to the yolk. 
