564 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



PLATE LI. 



(Stage XI.) 



FIGS. 183-186. Continuation of series of transverse sections of embryo begun on Plate L. x 74. 



FIG. 187. Part of sagittal section of similar embryo, cutting eyestalk somewhat obliquely. The 

 specimen was depigmented in nitric acid. The distal retinular cells, occupying the 

 spaces (Pg.c.) between tbe peripheral ends of the cones, are not represented. x305. 



REFERENCE LETTERS. 



oo. /'., accessory pigment cells. 

 <irf. m., adductor of mandible. 

 a. MI., superior .abdominal arteiy. 

 by., braucbiostegite. 

 '>. i'.. Mood vessel, 

 o. . crystalline cone. 

 eg., corneagen. 

 "I., octoderm. 

 end., cudoderm. 

 fg., foregut. 

 //., beart; 

 lit/., bypodcTiniN. 

 <m/<., intercepting membram-. 

 my., midgut. 



'nig.*, posterior lobe of midgut. 

 Mu., muscle of eyestalk. 

 If ii. c., extensor muscles of abdomen. 

 .1/n. /., flexor muscles of abdomen. 

 o. c. m., (L-sopbageal commissure. 

 Pg. C., position of distal retinular cells. 

 Ps., pericardia! sinus. 

 Rtu., proximal retinular cells. 

 Htu. 1 , nuclei of proximal retinular cells. 

 3, 4, ganglia of eyestalk. 



