REGENERATION 



425 



regenerative tissue. Feeding was shown to have no effect upon 

 the changes following irradiation. Whole specimens, irradiated but not 

 cut for regeneration, showed the deformations seen in later stages of head 

 and tail pieces. The worms sur- , , 



m^ash 



i^Tge. 



vived exposures up to 15 min. 

 without subsequent abnormali- 

 ties, but longer exposures re- 

 sulted in deformations which 

 presumably would have been 

 fatal in all cases. P. lugubris 

 again showed greater resistance 

 as whole individuals. With an 

 aluminum filter that cut out the 



beta and the softer gamma rays Fig. 8.— Cap of regenerative tissue on head- 



„ , and tailpieces of controls and irradiates oi 



there was much less etlect than Polycdis nigra exposed to radium 2 hr., as the 



with the unfiltered irradiation, cap appears 7 days after the operation when 



. , , time of exposure is varied. K, control. 1 H 



Many Ot the irradiates could Tj,e. to 5 r^e., exposures made at m to 5 days 



hardly be distinguished from the respectively after the operation of cutting into 



head and tail pieces. (From Weigand, 67.) 



controls. 



In the histological study, it was found that the cellular changes 

 induced by the irradiation could be recognized as early as 2 hr., whereas 

 external changes might not be recognized in such an individual until 



^^f. 





Uv5«ys.#«CV^ 



lsa: 



RZ' 



0k 



PhT 



Fig. 9. — Effect of radium upon cells of Polycelis nigra. Left — a sagittal section through 

 posterior end of a head piece, used as control and killed 4 days after operation, showing 

 normal accumulation of cells that form the cap of regenerative tissue visible externally. 

 Right — sagittal section through posterior end of an irradiated head piece exposed 6 hr., cut 

 immediately thereafter, and killed 6 days after such exposure and operation. Compare 

 the parenchyma with that shown in Fig. 5, right. There is no cap of regenerative cells. 

 The wound has been healed by extension of the old epithelium. Da, gut lobe; Ep, epithe- 

 lium; Pa, parenchyma; Ph, pharynx; PhT, pharynx sheath; Pig, pigment; RZ, regenerative 

 cells. (From Weigand, 67.) 



4 or 5 days after the exposure. In worms cut immediately after irradia- 

 tion of from 3 to 15 hr. (Fig. 9) healing occurred in the irradiates in the 

 same manner as in controls by extension of the old epithelium ; but there 



