138 C. M. CHILD 



The Id-pieces, on the other hand, which are usually largelj^ 

 within the second zooid, show a marked increase in the capacity 

 to produce eyes and normal heads. Here 34 per ceilt are normal, 

 58 per cent teratophthalmic and 2 per cent teratomorphic, a total 

 of 94 per cent with eyes. The controls then show a decrease in the 

 frequency of formation of eyes and heads in the posterior direction 

 along the axis of the first zooid, while at the anterior end of the 

 second zooid a marked increase in the frequency of eyes and heads 

 appears. 



Comparing the KCN-pieces with these, we see that in Ha 

 only 6 per cent are normal as compared with 84 per cent in la, 

 while 74 per cent are teratophthalmic and 10 per cent terato- 

 morphic, as compared with 16 per cent in la. The remaining 10 

 per cent of Ha are anophthalmic or headless while none of la are 

 of this character. Here then the effect of the KCN is a very great 

 decrease in the regulatory capacity and particularly in the fre- 

 quency of normal as compared with teratophthalmic heads. 



In lib no normal forms appear, 56 per cent are teratophthalmic 

 and 14 per cent teratomorphic, a total of 70 per cent with eyes, the 

 remaining 30 per cent being either anophthalmic or headless. 

 This total, 70 per cent, is almost exactly the same as the total 

 percentage of eyes, 72 per cent, in lb, but in lib 14 per cent of 

 this total are teratomorphic, moreover, lib shows 20 per cent of 

 headless forms, as compared with 8 per cent in lb. In short, the 

 differences between the control and the KCN-lot in the 6-pieces 

 are nowhere very great : any one of the differences alone would be 

 within the limits of error, which, as I have determined by compar- 

 ing parallel series, are from 10 per cent to 20 per cent, being higher 

 in the posterior than in the anterior pieces. Taken together, 

 however, the figures in the different columns show beyond a 

 doubt that the KCN decreases the regulatory capacity of the 6- 

 pieces, but they also show, when compared with the a-pieces, that 

 the decrease is much less than in those. Apparently the KCN has 

 less depressing effect on the regulation of the 6-pieces than on that 

 of the a-pieces. 



In He 2 per cent normal appear as compared with 10 per cent 

 in Ic: this difference by itself is not great enough to be regarded 



