DYNAMICS OF MORPHOGENESIS 



119 



regulation in ether becomes almost entirely a process of redifferen- 

 tiation as contrasted with regeneration in the stricter sense. The 

 data of one series are given. 



Series 92. November 4, 1908. Well fed worms 15 to 17 mm. 

 in length were used. The series consists of ten prepharyngeal 

 pieces comprising the region between the levels 1 and 2 in figure 

 18, and ten postpharyngeal pieces {3 and 4> fig- 18). So far as 

 the results can be tabulated they are given in percentages in 

 table 2. Since each lot consists of ten pieces the percentage 

 figures are ten times the number of pieces. The a-pieces in 

 the table are the prepharyngeal, the 6-pieces the postpharyn- 

 geal pieces. 



The table shows the differences in the pieces after twelve and 

 after eighteen days in ether. After twelve days one (10 per cent) 

 of the prepharyngeal pieces has a normal head, one a teratoph- 

 thalmic head and at least three pieces (30 per cent +) show a new 

 pharynx. Three other pieces are disintegrating at the anterior 

 end instead of undergoing regulation and will soon die. The post- 

 pharyngeal pieces at this stage show no heads and no pharynges. 



After eighteen days in ether only three pieces are alive in each 

 set. Two of the three prepharyngeal pieces are normal and one 

 teratophthalmic and all have pharynges, while of the post- 

 pharyngeal pieces two are normal as regards the head, but are 

 without pharynges and one is degenerating anteriorly. It is evi- 

 dent that regulation is less completely inhibited in the prepharyn- 

 geal than in the postpharyngeal pieces. Heads and eyes appear 

 earlier and pharynges appear only in the prepharyngeal pieces. 



A few figures will serve to supplement the tabulated data. 

 Figure 19 shows the prepharyngeal piece with normal eyes after 



