536 MBMOiKS OF THE :national academy of sciences. 



Plate XXXVII. 

 (Stages V-VI.) 



Fig. 92. Part of trausverse sectiou, showing the structure of the keel-shaped ventral plate, and 

 indicatiug the origin of inesoblast from the surface of the latter. x29i. 



Fig. !•.;{. Surface view of embryo with buds of uaupliar appeuilages. The intermediate area (St. A.) 

 is covered by a .single layer of ectoderm. The invagination of the mouth has not 

 yet appeared. Some nuclei of cells which lie immediately below the surface, especially 

 in the thoracic abdominal plate region, are represented. x291. 



Figs. 94-9.5. Transverse sections of embryo, belonging to the same series as Fig. 92, to illustrate 

 the structure of the thickening optic disks. Degenerating nuclear products («.', .s-.^, 

 Fig. 95) are present, and two cells are seen delaminating side by side in Fig. 95. 



REFERENCE LETTERS. 



A. (/), rmiiiiR-nt of first anteiiiui. 

 A. (11), nidiuient of SRCOiul antenna. 



Ab. P,, ventral j>late. ^ 4P 



f. M., i>roliferating area of optio ganglion. 

 Ect., ectoderm. 

 , Md., rudiment ol mandible. 



Mes., wandering cells (mesoblast) attached to ectoderm. 

 - O. G., rndiment of optio ganglion. 



0. D., optic disk. 



».', s.-, products of degenerating chromatin. 

 St. A., sternal area. 



T. Cd., transverse cord uniting optic disks. 

 T. C, w.andering cell ; I'. €.', w.andering cell degenerating. 



