524 C. M. Child. 



pressure, while during rest it assumed a more rounded form. 

 This change in form is doubtless due primarily to muscular con- 

 tractions; the decrease in transverse diameter in consequence of 

 muscular contraction during progression must produce pressure 

 in the direction of the longitudinal axis at the anterior end — and 

 at the posterior end also if this is a cut surface: this pressure must 

 bring about elongation of the new parts; hence the change of 

 form in these regions. There can be little doubt that this pres- 

 sure constitutes a factor in the outgrowth of new tissue from a 

 cut surface and the form which it acquires. If this is the case the 

 greater outgrowth in A and B may be due in part to the fact that 

 such pressure has been more frequent or perhaps greater in 

 amount than in C. The different degrees of contraction of the 

 cut surface in the different pieces are also very probably due to 

 this or other similar factors connected with motor activity. 



The appearance of eyes in A is probably due to the outgrowth of 

 nerves from the cut end of the cords and their union with the 

 epithelium. 



These five pieces, which were cut as nearly as possible at the 

 same level, afford a good illustration of the difficulty of complete 

 control of experiments of this kind. It is very probable that the 

 differences are due to slight differences in level of the cut or in 

 the extent of injury to the tissues posterior to the cut surface, but 

 it is impossible to determine with certainty whether this is the 

 case. The points of chief importance are, however, the occur- 

 rence of a considerable amount of anterior regeneration (in A and 

 B) in the absence of the ganglia and the somewhat greater degree 

 of motor activity in all of these pieces, and especially in A and 

 B, as compared with regions further posterior. In this connec- 

 tion it is also of interest to note that regeneration was more rapid 

 in A than in B and in B than in C as may be seen by comparing 

 the three sets of figures. Thirty-two days after section A (Figs. 

 1 8 and 19) had regenerated more than twice as much new tissue 

 as B (Figs. 22 and 23) and several times as much as C (Fig. 26). 

 But even in A regeneration is much less rapid and the total amount 

 is less than in pieces containing the ganglia. Comparison of 

 Figs. 2-5 and 8-10 with Figs. 15-18 will illustrate this fact. In 



