532 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk^ XXXV. 

 (Stage IV.) 



Fia. T.'). Median lougitudiiial section 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. xll5. 



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 autennie. x291. 



Fig. 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 whicli the plate is increased, and cells below the surface {Y. V.) which 

 pass into the yolk. x291. 



REFERENCE LETTERS. 



A. (i ), first antenna. 



Ab. P., ventral jilate. 



Ch., eggshell. 



C. M., pioliferatiug area of optic disk. 



ec, ec.i"^ ectodermic cells of ventral plate (Fig. yS). ec, (Fig. 80) ectoderuiic cell of o|itic disk. 



Ep., ectoderm. 



0. 0., 0. Z>'., optic disks. 



Eet , protoplasmic reticulum. 



T. Cd., transverse cord. 



r. B., yolk ball. 



T. C, Y. C'^, wandering cells. 



Y. S., yolk sphere. 



