276 



CHARLES RUSSELL BARDEEN. 



is the most puzzling process in the regeneration of these tail 

 pieces. 



The region of pharynx formation depends upon the condition 

 of the piece and the region of the cut. In individuals not 

 sexually mature if the cut be made posterior to the old pharynx 

 the new pharynx will develop slightly anterior to the center of 

 the piece (Fig. 1 1, B}. I have followed the development of a large 

 number of such specimens during a cool spell when the regen- 

 erative processes were somewhat slow, and the successive stages 

 in regeneration therefore well marked. The following notes in- 



FlG. 9. To illustrate the formation of a new axial gut lateral to the axis of the 

 original gut, after oblique section ; D. lacteum. Magnification, 17 diameters. The 

 regenerated intestinal branches are shown in black. 



Fi<;. 10. To illustrate the development of a head symmetrically about the end of 

 the axial gut and posterior to an anterior lateral slip which contained no nervous 

 system. Magnification, 17 diameters. 



dicate these stages. The number of hours given in each instance 

 shows the length of time elapsing after isolation of the pieces : 



Eighteen hours. The cut surface is covered with epithelium 

 and there is some accumulation of parenchyma cells near it. 



Thirty-eight hours. Further accumulation of cells near the 

 cut surface. 



Sixty-six hours. Anastomosis of the posterior intestinal rami 

 in the vicinity of the cut surface (Fig. n,A). Advance of nerve 

 fibers into the head anlage. In some specimens there is a slight 

 accumulation of cells in the vicinity of the future pharynx. 



Ninety hours. The accumulation of cells in the pharyngeal 

 anlage is more marked. Between the region of anastomosis of 

 the posterior rami and the pharyngeal anlage new intestinal 

 branches are being formed. The head anlage has advanced in 

 development. 



One hundred and fourteen hours. Considerable anastomosis 



