CELL DIVISION IN EGGS OF CREPIDULA. 



585 



Yiq 54. Exp. 915: Pressed during 2d and 3d cleavages in chief axis of egg 

 nearly equally into 1A 1 and 1A 2 ,^ which are^now forming micromeres of the 1st I 

 and ID are forming micromeres 



Fig 



Exp. 904: Pressed during 3d cleavage, the direction of which was changed 



instead of Inotropic as in typical eggs 



(shown 



Fig. 56. Exp. 915: Pressed in chief axis during the 4th cleavage, the chief result being the enlarged 



and 



PLATE XLVIL 



Effects of Pressure. 



In all figures except 57, 65, 66 the axis of pressure was m the direction of the egg 

 Fig. 57. Exp. 1003: Pressure parallel with the egg axis has produced 



meres. 



Fig 



preserves its original polarity and is dividing to form the first set of micro- 

 Exp. 1003: Pressure in the chief axis of the egg has led to the formation of the micromeres 



instead 



micromeres 



usual and the 1st set has subdivided giving off "turret" cells two of which (16 2 and Id 2 ) are much larger 

 than usual, while the other two (la 2 and lc 2 ) have been forced to the lower side of the egg. 



Fig. 59. Exp. 915: Pressure in the direction of the egg axis has led to the formation of eight macro- 



micromere 



Fig. 60. Exp. 915: Pressure in the egg axis during the 4th cleavage has caused the formation 

 larger micromeres than normal, especially in quadrants C and D, indeed the 2d division of C is nearly equ 

 giving rise to two macromeres; in the subdivisions of the 1st set of micromeres the "turret" cells (lo*-li 



are much larger than usual. 



Fig. 61. Exp. 915: In this case the pressure was probably applied after the formation of the 1st i 

 of micromeres which are normal; the 2d set is also normal except in quadrant A, where the macromere 1 

 divided nearly equally into macromeres 2A 1 and 2A 2 , and the former has divided into 2A l and 2a 1 . 



Fig. 62. 



1001 (1): Normal 



upper half then gave off a micromere of the first set (lc 1 ) which, judging by the shape 



form 



cell as in the other three quadrants. 



Fig. 63. Exp. 1004 (2) : Pressed during the 3d cleavage, macromeres A and D divided nearly equally 



formed a micromere 



(2c) 



Fig. 64. Exp. 1003 : Pressed during the formation of the 2d set of micromeres 



usual 



macromeres 



Fig. 65. Exp. 915: Compressed obliquely to the egg axis; macromere B being shoved under 

 micromere plate; macromere A formed a first micromere larger than normal, which has divided eqi 

 (la 1 , la 2 ), and then gave rise to a second "micromere," which is really a macromere (2A 1 ). 



Fig. 66. Exp. 1001 (1): Compressed parallel with the egg axis, B and D being shoved under 

 other cells; the 1st and 2d sets of micromeres are nearly normal; at its 2d division A divided nearly eqi 

 into 3A and ZA l , each of which has formed a micromere (2a, 2a) in a dexiotropic direction. 



Fig. 67. Exp. 1001 (3) : The cleavage is normal except that 4d is larger than usual, the resul 

 pressure in the direction of the egg axis; the cells of the ectodermal cross are stippled. 



PLATE XLVIII. 



Effects of Electric Current. 



Eggs subjected to electric current (except figs. 76, 77) but probably showing effects of pressure. 

 Fig. 68. Exp. 1104 (?): 5 mil. amp., 5 min. First maturation spindle; the mitotic figure is much 

 longer than normal, is central in the egg and the spindle fibres, centrosomes and astral rays are either lacking 



or very faint. The position is probably due to pressure. „ , . _ . . 



Fig. 69. Exp. 1121 (2): 5 mil. amp. 10 min., normal 31 hrs. Second cleavage spindles abnormal 



in position, first cleavage furrow incomplete, development stopped. 



Fig. 70. Exp. 1121 (2): Similar to preceding. 



Fig. 71. Exp. 1121 (2): Similar to preceding. 



Fig. 72. Exp. 1121 (2): Similar to preceding. . *»- 



Fig. 73. Exp. 1121 (2) : Two cells, one containing a complete amphiaster but without any chromatin, 

 the other containing two nuclei and one sphere, probably as the result of pressure at the close ot the ist 

 cleavage. . . , , , . 



Fig. 74. Exp. 1121 (2): Second cleavage spindle abnormal in position and division delayed m one 



blastomere. ... . „ 0+ . 



Fig. 75. Exp. 1121 (2): Three macromeres in a linear series, the middle one containing two separate 

 cytoplasmic areas, nuclei and spheres, the result of the suppression of the first cleavage, as mng^. 



Fig. 76. Exp. 1001 (3) : A pressure experiment included in this plate by mistake, showing eight 

 macromeres and eight micromeres. 



