EARTHWORM PHARYNX EPITHELIUM. 



made either laterally or ventro-laterally. If, now, the epidermis is 

 to provide cells for the regenerating brain, such cells must arise 

 from the uninjured mid-dorsal epidermis and pass through the 

 muscle layers to the region where the brain should develop, or else 

 they must migrate there from the lateral epidermal wound. Either 

 because of the severity of this operation or because of the weak- 

 ened condition of worms kept through the winter, very few of 

 these worms lived. One of the survivors was fixed after ten days' 

 regeneration. In sections (Fig. 6) through the brain region of 

 this worm the lateral location of the wound (w.) is recognizable 

 by a break in the muscle wall and the lack of differentiated gland 

 cells in the overlying epidermis. The wound is remote from the 

 brain fundament (br.f.) which is already clearly established in its 

 normal mid-dorsal position. While the break in the body wall is 

 filled with regeneration tissue (r.t.), this tissue does not extend 

 across the cephalic space to the brain fundament. In this opera- 

 tion the lateral nerves were left intact and there is no evidence that 

 the pharynx epithelium was injured at any place. Nevertheless, as 

 regards relation of brain fundament to the pharynx wall, we find 

 conditions here the same as in cases described above an undoubted 

 activity on the part of the dorsal pharynx wall, as evidenced by its 

 lack of the external connective tissue and muscular layer and by 

 continuity of the proliferating epithelium (/>..) with the regener- 

 ating brain (br.f.). The brain anlage appears as a mass of deeply 

 stained cells lying mid-dorsally in the course of a tract of fibers 

 which have grown across between the two commissures. Most of 

 these cells are of the characteristic nervous and epithelial type. 

 Interspersed with these are smaller nuclei of doubtful significance, 

 probably leucocytes and connective tissue elements. Since in this 

 case the epidermis as a source of new brain material is eliminated, 

 there remain two possible sources the pharynx epithelium and the 

 old nervous tissue. However much the latter may supply to the 

 new brain fundament, it is certain that the pharynx epithelium 

 plays an important part. 



While the evidence in a problem of this sort is necessarily in- 

 direct, since one can not watch the process of regeneration within 

 the living worm, but is compelled to rely on the study of fixed and 



