80 



STACINC OF AMPHIBIAN EMBRYOS 



RANA PIPIENS 



60. -61. Yolk exposed laterally on toil bud embryo. 



62. Persistent yolk plug prevents tail formation in toil bud stage. 



63. -66. Relation of persistent yolk to spina bifida. 



67. - 72. Spina bifida in various degrees. Note fair degree of head formation in some cases. 



