546 MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 



PLATE XLII. 



(Stage VI.) 



FIGS. 119-122. Serial transverse sections of the egg-nauplius, continued from PI. XLI. In Fig. 

 120 a transverse row of cells with large clear nuclei is seen. This is probably a 

 series of budding ectoblasts and mesoblasts, already referred to. Wandering cells 

 appear to be settling down upon all parts of the embryo. In the thoracico-abdonii- 

 iial fold (Fig. 122, MM.) the abdominal muscles are already undergoing differentiation 



out of the mesoblast of the ventral plate. x295. 



j 



REFERENCE LETTERS. 



A., anal invaginatiou. 



A. (II), anteunal bud. 



Ab., abdomen. 



A. Y. H., yulk undergoing change. 



R. /.., budding zone. 



Eel., ectoderm. 



HIJ., intestine. 



Md., maiidiblr. 



J/rf. (;., mandibular ganglion. 



Mt's., HK'soderiM. 



M. F., median groove. 



Mn., muscle cells. 



^[.r. (1), first maxillary bud. 



.', products of cell degeneration. 



S. C., degenerating cells. 



]'., yolk. 



Y. C., Y. C.', wandering cells. 



Vac., vacuole. 



