2l8 MIRIAM F. NUZUM AND HERBERT W. RAND. 



pharynx as there was in the seven-day stage. Some of the nuclei 

 in the region where the muscle layers have been repaired resemble 

 epidermal nuclei, but no mitosis can be observed in the epidermis. 

 Lying about midway between the epidermis and pharynx epi- 

 thelium is the brain fundament. Fig. 5 represents the median 

 region of the brain fundament and the neighboring pharynx epithe- 

 lium. Between the brain fundament (br.f.) and the pharynx epi- 

 thelium (/>.<?.) occurs a compact cell mass similar to that found in 

 a corresponding place in the seven-day stage. The dorsal pharynx 

 epithelium in this worm is still active. The non-epithelial tissue 

 of the pharynx wall terminates on either side, leaving the mid- 

 dorsal region of the epithelium in close relation to the new brain. 

 Throughout this series of sections mitoses (w.) are fairly abun- 

 dant in that part of the dorsal epithelium lying beneath the brain 

 fundament, but not elsewhere. The occurrence of these mitoses, 

 together with the presence of nuclei precisely like those of the 

 epithelial layer, but sub-epithelial in position (Fig. 5, s.n.}, affords 

 the best possible evidence that the pharynx epithelium is proliferat- 

 ing cells which are passing into the region of the regenerating 

 brain. Smaller nuclei, probably leucocytic in nature, are found 

 interspersed with these other nuclei. Some fibrous material (/.), 

 probably indicating the reestablishment of the muscle and connec- 

 tive tissue layer of the pharynx wall, and also blood vessels (bl.v.}, 

 are observed between the pharynx epithelium and the brain. 



In a nineteen-day stage the new brain has a normal shape, but 

 is not yet of normal size. Very little evidence of the wound re- 

 mains aside from the absence of differentiated gland cells in the 

 mid-dorsal epidermis. The wound in the muscle layer is barely 

 recognizable. Between the brain fundament and the pharynx epi- 

 thelium lies a compact cell mass as in earlier stages, but with some 

 indications of the establishment of the non-epithelial tissue of the 

 pharynx wall. Numerous cases of mitosis occur in the dorsal 

 pharyngeal epithelium. Several cases of mitosis within the brain 

 fundament demonstrate that the cells already there are increasing 

 in number. 



In order to put the epidermis at the greatest possible disad- 

 vantage as a source of material for the dorsal brain anlage, a 

 number of operations were performed in which the incisions were 



