MOUSE EMBRYO 



465 



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Head of mouse embryo at 18.5 days showing pronounced 

 exencephalia (brain hernia) following exposure to x-rays 

 at 8. 5 days gestation. 



Delayed cleavage at 2. 5 days after conception of the 

 mouse egg, showing the effect of x-irradiation at 0.5 days 

 (before the first cleavage) in the form of lagging and sticky 

 chromosomes, pyknotic nuclei, separation of cytoplasm of 

 adjoining cells. 



Implantation sites of nine mouse embryos, and one surviving 

 fetus following x-irradiation at 2. 5 days after conception. The 

 one survivor appears to be normal but was grossly stunted when 

 compared with the controls. 



One control (left) and three mouse embryos at 18.5 days, follow- 

 ing exposure of the three at 2. 5 days post -conception to 50 x-rays. 

 Note complete disorganization of all cephalic structures, and pro- 

 nounced stunting when compared with the control. 



