532 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



I'l.ATK XXXV. 

 (Stage IV.) 



Fiir. 75. Mediau longitudinal sectioii of the entire embryo. One of the wandering cells, which is 

 approaching the surface of the egg opposite the thoracic abdominal plate, is in the 

 process of division. xl!5. 



FIGS. 76-83. Consecutive serial transverse sections through the left optic disk of same, to illus- 

 trate the earliest stages in the thickening of the disks. The most posterior section 

 (Fig. 83) cuts the first pair of antenna?. x291. 



FKI. 84. Transverse section through the middle of optic disks, x 115. 



FIG. 85. Transverse section through thoracic abdominal plate, showing the multiplication of sur- 

 face cells, by which the plate is increased, and cells below the surface ( Y. C.) which 

 pass into tin- yolk. x-91. 



REFERENCE LETTERS. 







A. ( 1 ), first antenua. 



.4b. P., ventral plate. 



Ch., eggshell. 



C. M., proliferating area of optic disk. 



., /'I-.'-- 1 , fctoderniic rells of ventral plate (Fig. !*). ec., (Fig. 80) ectoderuiic cell of optic disk. 



KJI., I'rtoderin. 



O. O., O. D'., optic disks. 



Ret , protoplasmic reticiiluiii. 



T. I'd., transverse cord. 



Y. R., yolk ball. 



F. ('., Y. C.'~ 2 , wandering cells. 



T. S., yolk sphere. 



