DYNAMICS OF MORPHOGENESIS 117 



The head is usually normal as in figure 12, though occasionally 

 teratophthalmic. In these five pieces no appreciable changes 

 beyond the condition shown in figure 12 occurred before death. 



Figure 13 shows a piece cut after the worms had been four days 

 in alcohol and left in alcohol fourteen days after cutting. At 

 the end of this time four pieces were alive. As indicated in the 

 figure, regulation at the posterior end is limited to filling in the 

 contracted cut surface and the pharynx is also entirely absent. 

 Nevertheless these pieces form a head, though it is usually tera- 

 tophthalmic. Here again the formation of a head occurs under 

 conditions which inhibit the formation of pharynx and tail. 

 No further regulation occurred in these pieces and they finally 

 died in the alcohol. 



In general the same axial relations appear in this series as in 

 the preceding : the regulatory processes at the anterior end of the 

 piece are less retarded or less often inhibited than those concerned 

 with pharynx-formation and these in turn less than the processes 

 of tail formation. 



Series 69 and 70. In these series the effects of different concen- 

 trations of alcohol were compared. On August 4, 1908, pieces 

 including the old head and the region anterior to the level 2 in 

 figure 1 were cut from worms about 10 mm. in length. Of these 

 pieces five were placed in water as control, five in 0.5 per cent 

 alcohol, five in 1 per cent and five in 2 per cent alcohol. The 

 room temperature at the time of the experiment was rather high 

 during the day, of ten reaching 26^C. and regulation occurred rap- 

 idly. At the end of five days the pieces in water were approxi- 

 mately like figure 14. New tissue had grown out at the poster- 

 practically completed; the postpharyngeal intestinal branches 

 already extended well into the new tissue. Figure 15 shows the 

 usual condition after five days in 0.5 per cent alcohol. The 

 formation of the pharynx and of the two lateral intestinal branches 

 has taken place, but the posterior i^ew tissue does not form a 

 functional tail and the intestinal branches have not grown into it. 



Figure 16, from 1 per cent alcohol after five days, shows still 

 further decrease in the posterior new tissue. No tail is present 



