572 bulletin: museum of comparative zoology. 



would demonstrate that the development of the new head was in- 

 dependent of any mechanical support or stimulation furnished by 

 the tube. A still more rigorous test of the capacity for self-differen- 

 tiation of the cephalic organs would be provided by removing both 

 the digestive tube and nerve cord at the anterior end. 



Accordingly, the present investigations were undertaken to de- 

 termine whether the structures near the anterior end of an earthworm 

 can regenerate when (1) the digestive tube, and (2) the digestive tube 

 and nerve cord are absent in this end. For convenience these two 

 groups of experiments will be discussed separately. 



The histological changes involved in the normal regeneration of 

 the Annelida have been worked out in considerable detail (Hescheler, 

 '98; Michel, '98; Nusbaum, '02 and '04; Rand, '01 and '05; von 

 Wagner, '00; Ziehnska, '09; and others). 



1. First Group of Experiments. 

 Materials and Methods. 



The worms were anaesthetized in an aqueous solution of chloretone 

 or in carbon dioxide. The three or four most anterior segments were 

 cut off. Then, with a fine pair of scissors, a longitudinal incision was 

 made in the body wall on the dorsal side, and the digestive tube 

 excised from about five segments at the anterior extremity of the 

 remaining piece. Each operated worm was kept in a cold room in a 

 Stender dish and on clean, moist filter paper. This series included 

 two hundred and nine worms. Of these, one hundred and seventy- 

 seven belonged to the species Eisenia foetida, and thirty-two to the 

 species Helodrilus caliginosus. Seventy-six worms survived the 

 operation. Each one of these was killed and sectioned sagittally 

 when it showed a small regenerated knob or cone at the operated end, 

 or when it seemed probable that sufficient time had elapsed since the 

 operation for regenerative processes to have proceeded to the desired 

 extent internally. The animals were always thoroughly anaes- 

 thetized, by one or the other of the methods indicated, before the 

 anterior portion was cut off and immersed in the fixative. This 

 anaesthetization minimized the possibility of distortion of the re- 

 generated structures by muscular contraction when the tissues came 

 in contact with the fixing fluid. 



Several animals from which merely the three or four head segments 

 were removed by a transverse cut served as controls. 



