THE GUT OF NEBALIACEA 9 



large volume for storage. The walls of the sac are formed of a thin layer of pavement epithelium made up 

 of huge highly vacuolated cells with a striated border and an average diameter of o-i mm. (Fig. 5 A, B). 

 A very thin basement membrane lies behind them. 



The intestine is a very narrow tube lying dorsal to this sac (Fig. 7 A). In places the lumen is so 

 small that it is hardly distinguishable, but posterior to the end of the digestive sac it opens out into 

 a wider rectal region. A muscular sphincter separates it from a short proctodeum. No rectal gland 

 was found. 



D 



Fig. 5. A. Cells of the digestive sac in surface view. B. Same in section showing striated border. C. Section of the plated 

 side walls of the stomach showing the grooves in the chitin as it is laid down over each cell and the closeness of the opposite 

 walls of the gut : ch. chitin ; gr. intercellular groove in the chitin ; /. lumen of the gut ; n. nucleus. D. Surface view of the chitin. 



MUSCULATURE 



The musculature of the fore-gut of Nebaliopsis is shown in Fig. 6 C. The similarities to the other 

 Nebaliacea are striking. The oesophagus and stomach are sheathed in strong bands of circular muscles 

 [h.circ. and v.circ). These bands are many times thicker than the corresponding ones in Nebalia, 

 while the tissue between them and the chitin is comparatively much reduced. They cease abruptly at 

 the end of the fore-gut. 



Acting antagonistically to these circular muscles are the dilator muscles. The dorsal dilators (d.dil.) 

 are probably homologous with the anterior dorsal dilators [a.d.dil.) of Nebalia, as the groove muscles 

 which lie close to the dorsal ridge between the anterior horns of the stomach run between them and 



