548 MEMOIRS OF THE :NAT10NAL ACADEMY OF SCIENCES. 



PJ.ATE XLIII. 



(Stage VI.) 



Figs. 123, 124. Completion of series of transverse sections of oggnaiiplius. Cells marked jMes. 



probably represent eui]o<lerm in Fig. 121. The heart is being formed at abont this 



time out of mesoblast eells at 7/, Fig. XLiii, and the en<loderm forms a jdale between 



it and the central yolk (v, I'Mg. 133). x295. 

 Fig. 125. Median longitudinal section of same stage. Compare with Fig. 106. The thoracico- 



abdominal fold is now distinctly directed forward, an i is overgrowing the sternal 



area between it and the mouth. The stomodaium is a bent tube. x295. 

 Fig. 126. Transverse section, cutting proctodteum. From an embryo of about the same age as 



that represented in Fig. 106. x29.5. 

 Fig. 127. Transverse section of embryo and entire egg oa level with anus, showing wandering 



cells (T. C, r. C.'-'). x7i. _ 



REFERENCE LETTERS. 



J., auiil iuvaginatioii. 



Ab., abdomen. 



A. Y. S., altered food yolk. 



CVi., eggshell. ^ 



Set., Ep., ectoderm. 



Gl., ganglionic rudiment. 



H., rudiment of heart. 



Bg., intestine. 



Lb., labrum. 



Mb., embryonic molt. 



.!/««., mesoderm. 



Mo., month. 



Pd., region of proctod;eal invagination. 



«.,s'., products of cell degeneration. 



S. C, wandering cells, probably in early stages of degeneration. 



■S'. 0. G., rudiment of brain. 



St. A., sternal area. 



Std., stomoda-um. 



r., yolk. 



¥. C, Y. C.'--, wandering cells. 



Y. S., .yolk spherules. 



Vac, vacuole. 



