114 PROCEEDINGS OF THE ACADEMY OF [Feb., 



channel to the anterior two Umbs. At the upper end of the ascending 

 ilmb the lumen gradually becomes circular in section, and remains so 

 for the remainder of its course. In D. gyrociliatus Schmidt (1857), 

 and in D. apatris Korschelt (1882), have each described a proven- 

 triculus (Vormagen), which is simply an enlargement of the horizontal 

 limb of the oesophagus. In isolated individuals of D. conklini there is 

 an indication of such a structure in a slight dilation of this portion of 

 the oesophagus, but this dilation is apparently not permanent, but 

 merely temporary. 



The cells which form the walls of the oesophagus are relatively large, 

 and very similar, except in their size, to those of the body wall. Cor- 

 related with the shape of the oesophageal lumen in its ascending limb 

 is a marked difference between the height of the cells of the lateral 

 and the anterior and posterior walls, since the exterior of the cesophagus 

 in section preserves a regular oval or circular contour. Those which 

 form the anterior and posterior walls are low and cuboid, while those 

 composing its lateral walls are high, and, although rather irregular, 

 both in size and shape, may, on the whole, be considered columnar in 

 form (cf. figs. 3 and 23). The cells of the remainder of the oesophagus 

 are fairly regular both in form and size, usually cuboid, arranged in a 

 single layer. All of the oesophageal cells are clothed with a thin 

 cuticle, a continuation of that covering the body, and also bear long 

 cilia. These spring from distinct basal knobs, which form a uniform 

 layer a short distance below the cuticle, a narrow subcuticular layer 

 intervening. 



In many individuals a large number of the nuclei of the oesophageal 

 wall are undergoing a process of degeneration, some of the stages being 

 represented in figs. 31 and 32. The various stages of this process have 

 not been carefully studied, but it is evident that bound up with this 

 process, possibly resulting from it, is the expulsion of the cell from its 

 epithelium. Such a cell is shown in fig. 31. Two possible explanations 

 of this phenomenon present themselves. The function of the cells may 

 be that of secretion, and their degeneration and expulsion the result 

 of old age, like the "cellules deferment" of the mid-intestine of Lagis 

 koreni, described by Brasil (1904). On the other hand the degenera- 

 tion and expulsion of these cells may have for its purpose the libera- 

 tion of the cell contents, which have acquired digestive properties, in 

 the lumen of the oesophagus. This would then be an example of 

 holocrine secretion (Ranvier). 



Closely connected with the oesophagus is an organ which is common 

 to all members of this group, and variously termed "proboscis," 



