480 WM. A. KEPNER AND W. J. SCOTT 



LITERATURE CITED 



Dahlgren and Kepner 1908 Principles of animal histology, New York. 

 Graff, L. von 1909 Die Siisswasserfauna Deutschlands. IV. Turbellaria. 



Strudelwiirmer. I. Teil; AUgemeines und Rhabdocoelida. Jena. 

 Lankester, E. Ray 1901 A treatise on zoology. Part IV. London. 

 Kepner and Taliaferro 1916 Jour. Morph., vol. 27. 



PLATE 1 



EXPLANATION OF FIGURES 



1 Frontal section involving the entire pharynx, cc, cushion cells; GP, gland 

 pore opening into the lumen of the enteron; 1, the approximate plane through 

 which section, shown in figure 2, was taken. X 200. 



2 Obliquely transverse section. Approximate plane of this section shown 

 by line 1, in figure 1. The cushion cells {cc) are here shown on the ventral side 

 and extending laterally about the pharynx-base. Had the section been taken 

 through the cells cc and strictly at right angles to the axis, the cushion cells would 

 have appeared on all sides of the section of the pharynx. X 100. 



3 A section of a mature cushion cell; section taken eccentric to the axis of 

 the cell. N, nucleus ; a, b, and c, diverticula of lai'ge central cavity of the cushion 

 cell. X 1500. 



4 Two phases in the growth of cushion cells. A younger cell, which resem- 

 bles the general mesenchyme cell; B, older cell. At B, the intermediate stage 

 of growth, the nucleus {N) reaches its maximum size. X 1500. 



