DYNAMICS OF MORPHOGENESIS 139 



as important. But 64 per cent of He are teratophthalmic, as 

 against 28 per cent in Ic and 8 per cent teratomorphic as against 

 2 per cent in Ic. The total with eyes for lie is 74 per cent, for 

 le only 40 per cent. On the other hand, only 26 per cent of lie 

 are anophthalmic and headless, as against 60 per cent in le. 



The effect of the KCN on the c-pieces is a very evident inerease 

 in the regulatory capacity of the pieces. At first glance such a 

 result seems paradoxical, but as ^ matter of fact it is characteristic, 

 not only for KCN but for the anesthetics, when used in a certain 

 way. A full discussion of the reasons for this result in the c- 

 pieces is postponed to a later paper. At present it need only be 

 said that if the process of head-formation in these pieces were the 

 restitution of a missing part, i.e., if it were in direct correlation 

 with the processes in the other regions of the piece, such a result 

 would be impossible. If, on the other hand, the formation of a 

 new head in a headless piece represents the formation of a new 

 individual head first and a process which occurs in spite of the 

 other pants of the piece, then it becomes easy to understand how 

 under certain conditions a depression of the piece should increase 

 the frequency of head-formation. The formation of the new 

 head in a headless piece of Planaria is a process of exactly this 

 kind. The new head forms from cells which are involved in the 

 wound-reaction and whether a given piece shall form a head or 

 not depends on whether the region concerned in wound-reaction 

 becomes sufficiently dominant over other parts to be self -deter- 

 mining and to be able to grow at their expense. If the required 

 degree of dominance is attained a new head forms and reorganizes 

 the piece in the antero-posterior direction. If the two regions 

 remain more or less exactly balanced the piece remains headless 

 or anophthalmic and finally, if the old part remains the dominant 

 component and controls the new outgrowth a posterior end will 

 arise, irrespective of whether the cut surface is anterior or posterior. 



In the present series this 'inverse' or more properly differential 

 effect of the KCN appears clearly only in the c-pieces, while in 

 the h- and a-pieces a direct depressing effect appears. As a mat- 

 ter of fact, however, the two factors in the effect of the KCN, the 

 direct and the differential, are always present and the actual result 



