284 CHARLES RUSSELL BARDEEN. 



nating area of the nervous system of the piece. In most cases 

 of regeneration of a new head, this means the most anterior por- 

 tion of the old central nervous system. Lillie has stated this 

 point of view very clearly in the article referred to above. But 

 while the stimulus to brain formation arises from the chief coor- 

 dinating center of the piece, the head and the brain are symmet- 

 rically formed about a center of nutrition which is represented 

 by that portion of the intestinal system which lies immediately 

 adjacent to the nerve center, and which is in most direct con- 

 tinuity with the main intestinal apparatus. A symmetrical head 

 is formed both when the stimulus to brain formation comes from 

 one side and when it comes from both sides of this projecting 

 intestinal tip. 



There is an interesting correlation between the lateral nerve 

 cords and the eyes. In oblique pieces the most direct stimulus 

 to brain formation comes from that nerve cord which is the more 

 anteriorly situated. As a rule the eye on the side corresponding 

 to this nerve cord is developed earlier, and at first larger, than that 

 upon the other. This is still more marked in the regeneration 

 of oblique cross pieces divided in the median line, as shown by 

 Morgan (op. cit. 1901). So, too, in the regeneration of lateral 

 slips the eye on the outer side is usually earlier developed than 

 that on the median. 



That stimulus to brain formation depends upon the central 

 nervous system projecting into the area of the cut and that the 

 head is formed symmetrically about the tip of the axial gut, 

 with the cut surface as a base, is indicated by the following 

 experiment. If a longitudinal cut be made lateral to the nerve 

 cord from the region of the head back nearly to the pharynx, 

 and then transversely across the body, the slip thus left attached 

 to the main piece will contain none of the central nervous system 

 of the animal. The slip will contract posteriorly and will bend 

 over so as to become fused to the transverse cut surface. When 

 regeneration is well under way it will be found that the new 

 head is developing on the transverse cut surface, symmetrically 

 about the tip of the old axial gut, as shown in" Fig. 10. The 

 contracted anterior slip exhibits no specific influence on the 

 regeneration of the head, although the latter is continuous with 



