214 MIRIAM F. NUZUM AND HERBERT W. RAND. 



or " brain," be removed through a small incision in the body wall, 

 the operation being carried out so that no tissue other than nervous 

 is removed and with a minimum of damage to non-nervous tissues, 

 the resulting regenerative situation is much simpler. The non- 

 nervous tissues will require only a direct healing of the wounds 

 caused by the incision. If, under these circumstances, the brain 

 is regenerated, what will be the source of its material? 



Friedlander (1895) carried out operations of the latter sort. 

 He regarded the regenerated supra-esophageal ganglia as derived 

 mainly from the old nerve tissue, but perhaps partly from cells of 

 the wound tissue or " Regenerationsgewebe." He suggested that 

 these latter cells might be of leucocytic origin. Hiibner (1902) 

 repeated the experiment and concluded that leucocytes played little 

 or no part in the regeneration and that the epidermis was mainly 

 responsible for it. His figures show a mass of cells, with small 

 deeply stained nuclei, lying below the epidermis in the region of 

 the wound and extending down to the region of the developing 

 brain. But his figures and his scanty description do not afford 

 convincing evidence that these cells are epidermal in origin and are 

 actually contributing to the new brain fundament. Some time ago 

 the senior author found, in sections of earthworms regenerating 

 after an operation of this kind, indications that the pharynx x 

 epithelium might contribute cells to the regeneration of the nervous 

 organs of the head. Accordingly the study described below was 

 undertaken, partly for the purpose of obtaining more complete 

 data concerning the histogenesis of the brain following an opera- 

 tion in which no head segments are removed, and especially with 

 a view to ascertaining whether pharynx epithelium can produce 

 nerve cells. Involved in the latter question is another will an 

 epithelium which is not itself injured become active and participate 

 in regeneration? 



A wound is supposed to supply the stimulus for regeneration. 

 Therefore, with reference to the question as to whether an unin- 

 jured epithelium will engage in regeneration, the ideal operation 

 would have been to remove the brain without causing any other 

 injury to the worm. This being obviously impossible, the follow- 

 ing plan was devised. After narcotizing the worm in 0.2 per cent, 

 chloretone for ten minutes, an incision was made in the dorsal body 



