4 • REGENERATION 



When merely a lateral incision is made through the body wall 

 of Cerianthus (ahc, in Fig. 6), tentacles will grow out from the 

 lower edge be of the cut. No growth of tentacles will occur from 

 the other end, ah, and only the ordinary process of wound healing 

 will take place here as a consequence of which the incision will 

 be closed. The body of the animal will look after some time as 

 in Fig. 7. 



The sea water does not contain the material for the formation 

 of the new tentacles. The tentacles are formed from material 

 contained in the tissue sap which surrounds the cells and soluble 

 material in this sap is synthesized by an action inside the cells 



Fig. 6. Fig. 7. 



Figs. 6 and 7. — Effect of lateral incision into the body of the actinian. 

 the lower edge be of the incision abc forms tentacles. 



Only 



into the solid material forming the regenerated tentacles. Since 

 the chromosomes of the nucleus determine the hereditary form 

 their chemical constitution must in some way be responsible for 

 the formation of tentacles in the regenerating piece. 



As a second type may be selected the regeneration of fresh 

 water planarians studied by Morgan.^ When a piece, acdb 

 (Fig. 8), is cut out from a planarian at right angles with the longi- 

 tudinal axis of the animal the piece will regenerate a new head in 

 front of ac, a new tail at the other end, db, and an organism as 

 represented in Fig. 9 will result. When, however, the piece acdb 

 is cut out obliquely from the body (Fig. 10) a tiny new head will 

 be formed only in the foremost corner a, and a tiny new tail in 

 the hindmost end b (Fig. 11). This type of regeneration differs 

 typically from that of Cerianthus in that the regeneration is no 

 longer the same for each longitudinal element but depends upon 



1 Morgan, T. H.: "Regeneration," New York, 1901. 



