ON THE DIPLOCHORDA. 305 



region of the " stomach " has commenced, but the wall has 

 not yet begun to protrude. He refers to the area as the 

 "brown specks." 



Lastly, Wilson (22) figures these organs in several positions, 

 and refers to them as "glandular lobes of the stomach." 



It will thus be readily seen that the organs have been 

 repeatedly noticed by others, and a few sections could not 

 have failed to reveal their true structure. 



At its posterior end the pharynx becomes constricted, and 

 then leads into the true stomach. The walls of this part con- 

 sist, for the most part, of a single layer of hypoblast ; the 

 cells are cubical, with small cilia, and differ from the cells of 

 the pharynx in that the nuclei are not so regularly arranged 

 (PI. 19, fig. 17). In the ventro-lateral region on each side 

 they lose their cell walls, and are heaped up into two 

 ridges or mounds extending the whole length of the stomach 

 (PI. 19, fig. 17, d. a.). Each of these ridges consists of an 

 amoeboid mass of nucleated cells without cell walls. Thev 

 project some distance into the lumen of the gut, and there are 

 always embedded in them the residue of various food-particles, 

 usually surrounded by a clear vacuole. These ridges are their 

 special organs for intracellular digestion, and may be termed 

 the digestive areas. The mid-ventral wall of the gut between 

 them differs slightly from that of the rest of the stomach, the 

 cells being rather more columnar and numerous, and the 

 nuclei more regularly arranged. In addition to this a certain 

 portion of them, exactly opposite the " diverticulum" (PL 20, 

 fig. 20, V. ch.), undergo a modification into vacuolated tissue 

 in all essential respects like tiiat of the notochords ; but it 

 does not apparently extend beyond the two-vacuole-deep stage. 

 This area of chordoid cells is evidently developed as a sup- 

 porting tissue to the parts in this region. 



The stomach contracts to a small opening at its hind end 

 which leads into the intestine, a fairly long bent tube which 

 passes to the anus situated at the centre of the area sur- 

 rounded by the perianal band. The cells of the intestine 

 are single-layered, columnar, and ciliated, and call for no special 



