STAGING OF AMPHIBIAN EMBRYOS 



79 



41. MeduHar^' plate forming even with an extruding yolk plug. 



42. Normal yolk plug but gastrular surface rough, indicating early disintegration. 



43. - 46. Neumlae with extruding yolk plugs. If these develop the embryos have severe caudal abnormalities. 

 47. - 53. Hemi-embryos, due to incomplete invagination. 



54. - 55. Rudimentary abnormal embryos due to failure to incorporate yolk. 



56. Hemi-embryo in which there is slight development of the head region. 



57. - 59. Anterior end fairly normal in hemi-embryos, internal structures very abnormal. 



RANA PIPIENS 



