EARTHWORM PHARYNX EPITHELIUM. 217 



fundament and the pharyngeal epithelium. One merges uninter- 

 ruptedly into the other. 



Fig. 4 is a high-power drawing of that region of the pharyngeal 

 epithelium marked A' in Fig. 3, together with the neighboring por- 

 tion of the brain fundament. The connective tissue and muscle 

 which in the normal pharynx lie external to the epithelium (Figs, 

 i and 2, 11. p.) have entirely disappeared from this region of the 

 pharynx wall. Not only has the dorsal pharynx wall lost its ex- 

 ternal layer, but its epithelium shows signs of considerable activity. 

 Instead of being composed of tall columnar cells with fairly well- 

 defined walls, the epithelium has become syncytial. Its nuclei are 

 larger than the normal epithelial nuclei and more nearly spherical, 

 but, like the normal, show the usual prominent nucleolus. Two 

 mitoses appear in the part of the section drawn (Fig. 4, in.} and 

 numerous nuclei of the epithelial type lie in more or less deep posi- 

 tions. The whole appearance of this syncytial cell mass is indica- 

 tive of rapid cell proliferation. 



In sharp contrast with these conditions are those found between 

 the brain fundament and epidermis (see Fig. 3). The distance 

 between the brain fundament and the epidermis is very much 

 greater than that between the brain fundament and pharynx epi- 

 thelium. The mass of cells between brain fundament and epi- 

 dermis consists mainly of cells with small deeply stained nuclei 

 without prominent nucleoli, resembling therefore neither the epi- 

 dermal nuclei nor those of the brain fundament. They remind one 

 rather of leucocytes. Here and there within this mass is found 

 an occasional nucleus which is similar to those of the epidermis. 

 No mitosis could be observed in the epidermis. The presence of 

 mitosis at this stage in the pharynx epithelium and its absence in 

 the epidermis is significant. 



At a twelve-day stage of a case in which the wound was made 

 dorso-laterally, the brain fundament approaches normal form, con- 

 sisting of two enlargements connected mid-dorsally. The position 

 of the wound is readily distinguishable by the absence of differ- 

 entiated epidermal gland cells. The cut through the muscle layers 

 is now completely healed, but its location is marked by the presence 

 of more than the usual number of nuclei. There is no mass of 

 wound tissue extending from the healed epidermis down to the 



