l66 C. M. CHILD. 



of a single median eye-spot instead of two, bilaterally sym- 

 metrical in position, is much more frequent than in larger pieces. 

 With decrease in size all stages between the fully developed head 

 — i. e., as fully developed as it ever becomes in anaesthetic 

 media — and headless pieces can be obtained. 



All of these differences in regulation which are connected with 

 differences in size can be observed in water, but in the anaesthetics 

 they occur in much larger pieces than in water. 



V. The Effect in Relation to Region of the Body. 



The regional differences are similar in character to those ob- 

 served in water but some of them are more marked. In the 

 anaesthetics, for example, pieces from the middle region of the 

 body, even those as long as one fourth of the whole length, 

 almost always remain headless, while in water only very short 

 pieces from the middle region fail to produce heads. Pieces one 

 fourth the length of the body taken from the region immediately 

 behind the old head almost always produce heads in the anaes- 

 thetic as well as in water. In short, it is almost impossible to 

 inhibit head-formation in pieces from this region, though there is 

 not the slightest difficulty in inhibiting it completely in pieces of 

 the same size from the middle region. When we compare pieces 

 of the same size taken in sequence from the anterior end poster- 

 iorly, we find that the ability to form a head disappears much more 

 rapidly in anaesthetics than in water, but at the region of fission 

 it appears again in both media and the pieces from the posterior 

 region of the body, i. e., the pieces of the second zooid, so far as 

 they survive — they are like pieces of younger animals in being 

 more sensitive than pieces from other regions when first placed 

 in the anaesthetic, and in becoming more rapidly and completely 

 acclimated — produce a larger percentage of normal heads (that 

 is, normal for the medium) than pieces from any other region. 



Manifestly the comparison of pieces from different regions 

 shows much more clearly than any series of experiments in water 

 that the ability to form certain parts is present in very different 

 degree in different regions of the body, and since the effect of the 

 anaesthetics is to depress the metabolic processes or certain of 

 them, the ability to form certain parts is apparently closely con- 

 nected with the intensity of certain metabolic processes. 



