FIELDS AND GRADIENTS 



303 



exert any morphogenetic effect on the old tissues of the stump : if, 

 as usually occurs, a complete appendage is restored, this is effected 

 entirely by means of new growth. 



y V 



J K L • I M 



Fig. 143 

 Differential susceptibility in Plmiaria dorotocephala. A-E, Various grades of 

 head differentiation after regeneration. A, Normal, B, Teratophthalmic (eyes 

 approximated or partially fused, head form nearly normal). C, D, Teratomorphic 

 (single median eye, lateral sensory projections approximated or fused anteriorly). 

 E, Anophthalmic (no eye, median or no sensory projection, rudimentary cephalic 

 ganglion). F-H, Diagrams showing, between the dotted lines, the regions 

 missing in hypotypic heads. F, In teratophthalmic forms (cf. B). G, In terato- 

 morphic forms (cf. C, D). H, In anophthalmic forms (cf. E). J-M, Differential 

 acclimatisation. J, Normal head. K, Reduction of apical region after 2-3 weeks 

 in dilute anaesthetics. L, M, Subsequent hypertrophy of the apical region after 

 iJ-2 weeks more in the solution. (Redrawn after Child, bidividiiality in Or- 

 ganisms, Chicago, 1915 (A-E), and jfoiirti. Exp. Zool. xxxiii, 1921 (F-K).) 



For this to occur, it is clear that exactly those regions removed 

 by the operation must be restored by the new growth, a phenome- 

 non abundantly confirmed in limb -regeneration in Arthropods and 



