Studies on Regulation, 



269 



larger than the other. In each case where the cut separated the 

 ganglia into halves or nearly so each half regenerated the other 

 half and each of the two heads was similar to other cases of lateral 

 regeneration in this region (Child, '04c). It was necessary to 

 repeat the operation of longitudinal splitting from three to five 

 times in order to prevent union of the two parts. 



Fig. 24 shows the anterior portion of the specimen in question 

 after the operation of splitting had been performed three times. 

 At this stage the operation was repeated for the last time. At the 

 next examination, a week later, it was found that the cut surfaces 

 resulting from the last opera- 

 tion had united in a somewhat 

 unusual manner (Fig. 25). The 

 right margin of the left head 

 overlapped the left margin of the 

 right head. It is evident from 

 Fig. 25 that the left margin of the 

 right head is giving rise to an 

 outgrowth in the posterior direc- 

 tion which is situated ventral to 

 the original body; in other words, 

 from that part of the cut surface 

 on the right head which did not 

 unite with the opposing surface, 

 a tail is regenerating. 



In Fig. 26 the new posterior end 

 has elongated still further. It 

 functions in all respects like the 

 typical posterior end of the 

 species. The animal uses it for attachment in creeping in the same 

 manner as the posterior end of the main body. Since the right 

 head is the dominant head of the specimen the functional activity 

 of this accessory posterior end is fairly coordinated with that of 

 the other parts of this head. 



It will be noted from the figure that the right margin of the left 

 head continues ventrally on the right margin of the new posterior 

 end and the left margin of the right head is continuous with its left 

 margin. The peculiar relations of this part to the other parts of 

 the specimen make it especially interesting. It is highly probable 

 that the attachment to the substratum of this part of the margin 



