22O MIRIAM F. NUZUM AND HERBERT W. RAND. 



sectioned material, nevertheless, in the twenty-five worms which 

 were carefully studied, the following facts stand out significantly : 



1. While there is evidence in some cases that the epidermis is 

 contributing cells to the regenerating brain, there is much more 

 evidence of the same kind that the pharynx epithelium is con- 

 tributing. 



2. In nearly all cases the brain fundament is in closer relation to 

 the pharynx epithelium than to the body wall. 



3. An uninjured dorsal epidermis does not become active and 

 contribute to the new brain, while an uninjured dorsal pharynx 

 epithelium does. 



4. When the incision is made decidedly laterally, there is no 

 evidence of migration of cells from the wounded epidermis to the 

 new brain. 



5. It is certain that the old nerve cords contribute some material 

 to the regenerated brain. Just how much it is impossible to say. 



6. The cells which seem to be passing from the pharynx epi- 

 thelium into the brain fundament have nuclei precisely like those 

 of cells which, in the later stages of regeneration, are certainly to 

 be identified as neuroblasts. 



If, as all the evidence described above clearly indicates, the 

 pharynx epithelium of the earthworm plays a large part in the 

 regeneration of a central nervous organ, we have here the phe- 

 nomenon of a tissue specialized for one purpose giving rise to one 

 highly specialized for another and very different purpose. Still 

 more remarkable is the fact that the pharynx, which in ontogeny 

 has nothing to do with the origin of the nervous organs, should, 

 upon removal of the brain, become an important source of material 

 for its regeneration. The only morphogenetic relation between the 

 old nerve tissue and the pharynx epithelium is that both are ecto- 

 dermal in origin, since the latter develops by invagination of ecto- 

 derm. 



This case resembles very closely the regeneration of the sala- 

 mander's lens as demonstrated by Wolff's (1894, 1895) experi- 

 ments on Triton. The lens, which in ontogeny is formed by a 

 thickening and invagination of ectoderm, is regenerated from the 

 upper edge of the iris. It can hardly be imagined that, in nature, 

 an earthworm accidentally loses a brain or the salamander a lens. 



