DYNAMICS OF MORPHOGENESIS 



65 



the character of the head to the normal, as well as the increase 

 in head-frequency, is also evident. In Lot II only 4 per cent of 

 normal heads appears, but in Lot III 28 per cent are normal, 

 in Lot IV, 76 per cent and in Lot V, 80 per cent. This series 

 shows that head determination begins almost at once after sec- 

 tion and that in most pieces, the head is fixedly determined 

 within seven to eight hours after section (Lot III, 88 per cent 

 form heads). 



The following series gives in general the same results but brings 

 out some points more clearly than the preceding. 



TABLE 2 



Series J^65. From well-fed worms 15 to 16 mm. in length, about 

 150 long piieces like ae (fig. 1) were cut. 



Lot I. Twenty-five short pieces {ah, fig. 1) cut immediately 

 after first operation. 



Lot 11, Twenty-five short pieces cut 2| to 3 hours after first 

 operation. 



Lot III. Twenty-five short pieces cut 5^ to 6 hours after first 

 operation. 



Lot IV. Twenty-five short pieces cut 12 hours after first 

 operation. 



All lots kept at 20 to 22°C. The results appear in table 2, in 

 percentages. 



The controls, i.e., twenty-five of the long pieces, all form heads, 

 72 per cent normal and 28 per cent teratophthalmic. On the 

 other hand, Lot I, consisting of twenty-five of the short pieces 

 removed at once from the anterior end of the long piece, develops 

 no heads at all, 96 per cent being headless and 4 per cent dead. 



