422 



BIOLOGICAL EFFECTS OF RADIATION 



m.f: 











N.S. 



12 days 





F.C. 



1 doiy 12 da^/s 



Fig. 4. — Inhibition of regeneration and destruction of formative cells in Planaria agilia 

 by X-raya. Ep, epithelium; F.C, formative cells; G, gut; M.F., muscle fibers; N.S., 

 nucleus of syncytium; S, syncytium. {From Curtis, 13.) 



Fig. 5. — Microphotographs showing effect of X-rays (3500 r) upon formative cells of 

 Planaria agilis. Left — part of a longitudinal section of control showing many formative 

 cells in parenchyma. Right — similar section of an irradiate 10 days after exposure showing 

 parenchyma without formative cells but with the syncytium, muscle fibers, etc., intact; 

 lobes of the gut and part of nerve cord are seen. Compare with Fig. 4. 



