534 MEMOlliS OF THE NATIONAL ACADEMY OF SCIENCES. 



PLATI: XXXVI. 

 (Stage V.) 



FIGS. 86, 87. Parts of longitudinal sections ol' embryo seven or eight hours older than that shown 

 in Fig. 71.'. The optic disk (0. D.) is cut in Fig. 86, and in Fig. 87 its inner part is 

 involved, with the outer border of the thoracic abdominal plate. There is no sharp 

 demarcation between the protoplasm and tlie yolk, as is indicated by the dotted lines 

 under the embryonic layers. x201. 



Fi<;s. SS-S9. Longitudinal serial sections through the entire embryo, somewhat younger than the 

 last, and six hours older than that represented in Fig. 72. The optic disk is sectioned 

 in Fig. 90 through its central proliferating area (C. M.), and the rudiments of the 

 three naupliar appendages appear in Fig. 811. x 115. 



Fie. 91. Transverse section cutting optic disks of embryo about nineteen hours older than that of 

 Fig. 72 and twelve hours older than that represented by Figs. 86, 87. Wandering 

 cells ( Y. C. 1 ) have traveled, to remote parts of the surface, and karyokinetic figures 

 (Y. ('.-', Fig. 89) prove that they are in active division, x 115. 



s 



REFERENCE LETTERS. 



,1. ( / ), rudiment, of lirst antenna. 



.1. (// ), rudiment of second antenna. 



All. I'., ventral plate. 



.Ijiji., area, of appendages. 



O/i., eggshell. 



C. M., proliferating area of optic disk. 



., migrating cctolilast cell. 



EI>. , ectoderm. 



Mel., rudiment of mandible. 



<>. !>., optic disk. 



., product of degenerating chromatin. 



$t. .1., sternal area. 



7'. Ctl., transverse cord. 



)". <.'., F. C. l -'\ wandering cells. 



F. 6'., yolk sphere. 



