NEMERTEANS 



241 



is almost as thick as the longitudinal layer of muscles and between two and four times as 

 thick as the basement membrane and circular muscles together. These last are about 

 equal in thickness. There are many large gland cells in the epithelium ; they may be the 

 black specks of the living animal. The sickle-shaped bodies similar to those first de- 

 scribed by Marion (1872) are found in the epithelium of all forms ; they appear to resist 

 acid and are yellowish brown in colour (Fig. 14). The fibre-containing basement mem- 

 brane stains deeply with haematoxylin, and numerous minute ducts can be seen pene- 

 trating it, especially on the head. Often the glands are themselves in the membrane but 

 sometimes they are more deeply placed in the longitudinal muscles. Farther down the 

 body they are much less frequent. 



-{£=■- cm 



Fig. 13. Zygonemertes capensis, n.sp. Head, dorsal Fig. 14. Zygonemertes capensis, n.sp. Part of a 



surface, cleared in anilin oil to show the three transverse section highly magnified, e, epithelium 



groups of eyespots. containing sickle-shaped bodies; bm, basement 



membrane; cm, circular muscle layer; /?«, longi- 

 tudinal muscle layer. 



The oesophagus opens into the rhynchodaeum before the brain. In the region of the 

 ganglia the oesophagus widens. Farther back it opens into the stomach with dark- 

 stained granules in the cells of the folded walls and on each side appears a branch of the 

 anterior caecum. These two diverticula do not reach the brain. 



There is a vascular loop in the tip of the head. In the brain region the lateral vessels 

 are widened, their walls become definite and they are connected with the dorsal vessel 

 above the gut. The three vessels pass down the body and join again above the gut just 

 before the insertion of the rhynchocoel into the body wall. The excretory vessels he 

 above the lateral nerves behind the brain. A single duct on each side opens to the ex- 

 terior opposite the nerves. The ganglia are not peculiar, but the brain is rather large 

 ( Fig . 1 5 A) . The lateral nerves give off branches which pass round the rhynchocoel , and at 

 the posterior end of the body they join above the gut anterior to the anus. The cerebral 

 canals open ventro-laterally a little way behind the opening of the oesophagus into the 



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