DYNAMICS OF MORPHOGENESIS 115 



the pharnjTx is minute and never attains anything like the usual 

 size in water. Figure 9 shows one of the more extreme cases in 

 which the head is smaller and teratophthalmic and the pharynx is 

 entirely absent. In all cases pharynx-formation is inhibited 

 before head-formation; the latter can go on to a greater or less 

 extent under conditions which completely inhibit the former. 



This series does not afford a direct comparison between the 

 pharynx and the posterior end because in the a-pieces the old 

 pharynx and in the 6-pieces the old posterior end is present. It 

 does show, however, that in the a-pieces head-formation may occur 

 under conditions which inhibit the formation of a posterior end 

 and in the 6-pieces under conditions which inhibit pharynx-forma- 

 tion. Moreover, we see that head-formation is affected to a 

 greater extent in the b- than in the a-pieces by a given concen- 

 tration of alcohol. All of these facts indicate the existence of 

 differences of some sort, apparently quantitative, in the dynamic 

 processes at different levels along the axis, both in the original 

 animal and in the piece. 



Series 84 and 85. October 12, 1908. Well fed worms 12 to 14 

 mm. in length were used. Series 85 consists of twenty pieces 

 including the old head and that portion of the body anterior to 

 the level 4 in figure 1: these were kept in 1.5 per cent alcohol. 

 Series 84 is a control of twenty similar pieces in water. Figure 

 10 shows the condition of the pieces of series 85 after eight days 

 in alcohol, figure 11 the condition of the control in water after 

 the same length of time. In figure 10 regulation posterior to the 

 new pharnyx is almost completely inhibited ; no tail is formed and 

 the postpharyngeal region does not elongate as in the control. 

 The pharynx itself is of small size, but its formation is not in- 

 hibited. Evidently postpharyngeal regulation and tail-formation 

 are more completely inhibited in this series than pharynx-forma- 

 tion. 



Series 81. In this series the effect of placing the whole worms 

 in alcohol for different lengths of time before operation was deter- 

 mined. On October 1, 1908, one hundred well fed worms 15 

 mm. in length were placed in alcohol 1.5 per cent in crystallizing 

 dishes holding about 1| liters: these were filled almost full of the 



