Studies on Regulation. 



515 



removed, so that regeneration of a large part of the head requires 

 only a slightly longer time than regeneration of a small part. 



Figs. 2-5 illustrate the course of anterior regeneration after 

 removal of the anterior portion of the head by a cut at the level 

 of the transverse line in Fig. i. In this series (Series 16, 

 August 16, '02) ten specimens were subjected to the operation 

 and the results obtained were essentially similar in all. After 

 section the cut surface contracts and becomes concave (Fig. 2). 

 Six days after section (Fig. 3) a mass of new tissue with convex 

 margin is visible on the cut surface. Fourteen days after section 

 (Fig. 4) this mass has increased in size and is approaching in 

 form the normal head. Eighteen days after section (Fig. <^) 



regeneration is practically completed. Some slight increase in 

 the new tissue may occur after this time but it is not sufficient 

 to alter the measurements to any marked extent. The distribu- 

 tion of the intestinal branches in the new tissue is only slightly 

 less complete than in the normal animal (not shown in the figures). 

 Comparison of the figures shows that the old cut surface has 

 become less concave during regeneration until in Fig. 5 it is 

 nearly a plane surface again. Numerous other specimens sub- 

 jected to similar operations afforded similar results. 



The behavior of these pieces during regeneration is, as might 

 be expected, similar in most respects to that of normal animals. 

 There is, however, a characteristic difference in the use of the 

 mutilated head. The continual searching movements of the 



