118 BULLETIN: MUSEUM OF COxMPARATIVE ZOOLOGY. 



4. Origin op the Cells of the Nervous Fundaments. 



According to Hescheler the cells which give rise to the regenerated 

 brain and ventral ganglia are derived chiefly from the epidermis. The 

 cicatrix is at first composed of lymph cells and spindle-shaped cells of 

 doubtful origin. Later appear cells with nuclei like those of the epi- 

 dermis. These he believes to be derived chiefly from the epidermis, 

 but some may come from the alimentary epithelium and some from cer- 

 tain large nuclei found in the muscle layers. In addition to these 

 sources there is mitosis within the old nerve cord which doubtless gives 

 rise to cells that assist in the regeneration. 



From my own preparations similar conclusions as to the origin of 

 the regenerated nervous elements must be drawn, except that only in 

 rare cases is there any evidence that cells of the old cord assist in the 

 regeneration. 



In the preparation from which Figure 14 is taken, the cicatrix {cic.) is 

 a solid mass composed mainly of greatly elongated spindle-shaped cells 

 with small oval or elongated nuclei. Figure 17 represents a number of 

 these cells more highly magnified. The nuclei are totally unlike epi- 

 dermal nuclei, being much smaller, of different shape, and lacking a 

 prominent nucleolus. Epidermal nuclei drawn to the same scale as 

 Figure 17 may be seen in Figures 43-45 (Plate 6). There are also pres- 

 ent in the cicatricial mass some very small spherical nuclei. These are 

 doubtless nuclei of lymph cells, for they present exactly the appearance 

 of the nuclei of the lymph cells commonly found in the body cavity. 

 These lymph cells, in some preparations, are much more numerous in 

 the regenerating region than elsewhere, often occurring in almost solid 

 masses. 



There is individual variation as to the character of the cicatrix. In 

 most of my preparations of early stages (7 to 11 days) the cicatrix was 

 composed chiefly of the spindle-shaped cells. In one eleven-day pre- 

 paration, however, there was only a small mass of cells underlying the 

 regenerated epidermis, and this mass was composed mainly of cells with 

 large nuclei having all the characters of epidermal nuclei. These cells 

 wei-e actively dividing. Figure 57 (Plate 8) shows a group of these 

 nuclei. 



According to Hescheler the spindle cells give rise to the new muscle 

 layers. In my preparations of later stages, too, these spindle cells are 

 seen to be taking the direction of the fibres of the two muscle layers in 



