206 \V. E. ALLEN. 



EXPLANATION OF PLATE I. 



All figures are from camera drawings and partly diagrammatic. All have the 

 same magnification (375 diam.)- None are intended to represent cell detail. 

 All show only most conspicuous features of the ventral side in or near the tenth 

 regenerated segment. 



FIG. i. Third day. Septa almost formed. Muscles just distinguishable. 

 Proliferation of epidermis and embryonic cells just inside muscle layer. 



FIG. 2. Fourth day. Septa formed. Epidermal proliferation less. Cells 

 massing to form nerve cord inside the muscle layer. 



FIG. 3. Fifth day. Nerve cord, bloodvessel and peritoneum formed. No 

 proliferation. 



FIG. 4. Ninth Day. Typical ventral localization of cells in ner%-e cord. 



FIG. 5. Old, mature segment. Note larger size, the thin epidermis and thick 

 muscle layer. 



FIG. 6. Eighth day. Optical section. Immature nephridium. Mature seta 

 sac and muscles. 



