BIGELOW. Development of Lepas. 



PLATE 8. 



All figures drawn from sections ten micra thick. Vegetative (ventral) pole and 

 blastopore at the left in views of sagittal sections. 



Fig. 66. Parasagittal section of eight-cell stage, a little to the left of the sagittal 

 plane, and corresponding to the stage shown in Figure 40 (Plate 5). 



Fig. 67. Section, in same plane, of stage with fifteen blastoderm cells ; the yolk- 

 cell still in the stage of fourth cleavage. This stage corresponds to 

 that of Figure 41. 



Fig. 68. Parasagittal section of sixteen-cell stage, corresponding to that shown in 

 Figure 45. 



Fig. 69. Sagittal section of egg with twenty-eight cells in blastoderm ; primary 

 mesoblast cell (c? 5 - 2 ) in division ; entoblast nucleus preparing to divide. 

 Compare with Figures 49, 50 (Plate 6). 



Fig. 70. Horizontal section of same stage, seen from vegetative pole. 



Fig. 71. Sagittal section of sixty-two-cell stage, counting two dividing primary 

 mesoblasts (c? 6>3 , c?' 4 ) as four cells. Same age as Figure 56 (Plate 7). 



Fig. 72. Transverse section of egg in similar stage cut through the primary mes- 

 oblasts and the posterior pair of "secondary mesoblasts" (a 7 ' 5 , c 7 ' 5 ). 



Fig. 73. Section immediately anterior to the one represented in the preceding 

 figure. The anterior " secondary mesoblasts " (6 7>5 , 6 7 ' 7 ) and the two 

 entoblast cells (rf 6>1 , c? 6 * 2 ) are represented. 



