288 C. M. CHILD 



The third eighth varies in character: it may be a teratopthalmic 

 whole of the character of fig. 25, or very rarely it may be a 

 normal whole, but commonly it is headless like fig. 26, usually 

 with an anterior regenerate of considerable size, but without any 

 of the characteristics of a head. The posterior regenerate is 

 also large. Such headless pieces undergo change in shape much 

 less rapidly than wholes: figs. 24, 25 and 26, for example, repre- 

 sent pieces after the same length of time since isolation. 



The fourth and fifth eighths are practically always headless 

 (fig. 27) and the size of the anterior regenerate usually decreases 

 from the third to the fifth. In the fifth eighth the new pharynx 

 is anterior to the middle, (fig. 27) 



The seventh eighth (fig. 28) is, on the other hand usually a nor- 

 mal whole with anterior regenerate ending anterior to the eyes 

 and pharynx in the middle of the body. The sixth eighth is most 

 commonly headless like the fifth, but sometimes forms a terato- 

 pthalmic whole, or more rarely a normal whole like the seventh. 

 The most posterior eighth almost always forms a normal whole 

 like the seventh (fig. 28), rarely it is teratopthalmic but never 

 headless. 



In these eighths we see the results of regulation running from 

 normal wholes at the anterior end to headless forms in the middle 

 region and then in the posterior fourth suddenly becoming nor- 

 mal wholes again. The differences in size of head, shape of body, 

 amount of regeneration and position of the pharynx are similar 

 to those in the fourths, but more extreme. 



Sixteenths. Fig. 17, ab, be, cd, de, etc. The first sixteenth 

 after removal of the head is commonly tailless with relatively 

 very large head (fig. 29), though it may sometimes produce a 

 normal whole of the type of fig. 30. The second sixteenth pro- 

 duces either a normal or a teratopthalmic whole of the general 

 type of figs. 30 and 31. The third sixteenth may produce a nor- 

 mal whole (fig. 30), a teratopthalmic whole (fig. 31) or even a 

 headless tail (fig. 32): like the third, the fourth sixteenth may 

 produce normal or teratopthalmic wholes or headless tails, but 

 usually the percentage of headless tails is higher than in the third. 



