404 PROCEEDINGS OF THE ACADEMY OF [April. 



Fig. 48. — Same oo;g as fig. 45, lateral view of C. quadrant. ■ 

 Fig. 49. — Lateral view of D quadrant in egg of about 86 cells. 2d^-^ is 

 dividing Ineotropically ; 2d-" and 2d-^'- have divided dexiotropically. 

 Fig. 50. — Lateral view of same egg as fig. 49, showing A quadrant. 



Plate XXVII, Fig. 5L — D quadrant, a lateral view. Me' and Me^ all dividing 



bilaterally. 

 Fig. 52. — Lateral view, B quadrant of same egg as fig. 49. 

 Fig. 53. — Upper pole view of egg of about 86 cells. The "apical" (la"'- 



ld"i) and "peripheral" (la"--ld''-) rosettes have been formed bj- 



Iseotropic cleavages. 

 Fig. 54. — Same egg as fig. 51, seen from side (C cjuadrant). 

 Fig. 56. — Upper pole view of an egg of approximatelj^ 106 cells. The basal 



cells, la'-', lb'=', Ic'^', have divided; ld'=' is dividing with spindle 



transverse to posterior arm of cross. The two inner jjosterior 



trochoblasts (Ic-', Id-') are dividing bilaterally. 

 Fig. 57. — Vegetative pole view of same egg as fig. 56. Completed division 



of Me', Me- into M'e', M-e- and m'z', m-z-. 

 Fig. 58. — Same egg as fig. 56, showing A and D cjuadrants on lateral view. 

 Fig. 59. — Same egg as fig. 56, principally B quadrant. 



Plate XXVIII, Fig. 60. — Same egg as fig. 56, lateral view of C quadrant. 



Fig. 61. — Lateral view, D quadrant, same egg as fig. 56. 



Fig. 62. — Upper pole -siew of egg slightly older than last series (over 115 

 cells). All the interior trochoblasts have divided, and the completed 

 transverse di\'ision of the basal cell of the posterior arm of the cross 

 is shown. 



Fig. 63. — Same egg as fig. 62, showing A quadrant on lateral view. 



Fig. 64. — Lateral view, same egg as fig. 62, B cjuadrant. 



Fig. 65. — Lateral view, same egg as fig. 62, C quadrant. 



Fig. 66. — Lateral view, same egg as fig. 62, D cjuadrant. 



Fig. 67. — Egg of about 125 cells, lateral view, C quadrant. 



Plate XXIX, Fig. 68. — Same egg as fig. 67, lateral view of A quadrant. 



Fig. 69. — Same egg as fig. 67, lateral view of B quadrant. 



Fig. 70. — Slightly later stage than fig. 67, lateral view of C quadrant. 



Fig. 71. — Entomeres and mesomeres from egg of o\'er 150 cells, seen from 

 vegetative pole. 



Fig. 72. — Entomeres and mesomeres of egg aljout stage of fig. 71. 



Fig. 73. — Entomeres and mesomeres, seen from vegetative pole of egg slightly 

 older than the two former stages. 



Fig. 74. — "\'egetative pole view of about same stage as fig. 73, showing the 

 overgrowth of the "secondarv" mesoblasts (ecto-mesoblasts, 3a-'", 

 3a-2ii, 3b="', 3b"") by other cells of the third quartet. 



Fig. 75. — L'pper pole view, about the same stage as fig. 74, showing trans- 

 verse splitting of the arms of the cross and division of outer trocho- 

 blasts. 



Plate XXX, Fig. 76. — Upper pole view of somewhat later stage than fig. 75. 



showing increase in breadth of cross area. 

 Fig. 77. — Lateral view of stage similar to fig. 75, showing large excretory 



cell (3c"") and neighboring cells. 

 Fig. 78. — Vegetative pole view of gastrula with closing blastopore, showing 



pointed anterior end and complete overgrowth of the ecto-mesoblast. 

 Fig. 79. — Somewhat older gastrula than preceding figure. 

 Fig. 80. — Optical section (parallel to ventral surface) of gastrula of about 



the stage shown in fig. 79. 



Plate XXXI (except figs. 81-S). Figs. 81-84. — Optical sections, similar in direc- 

 tion to that of fig. SO, through successively older gastrula^, showing 

 torsion of the enteron through increase in area of the left side (right 



