TWO NEW BRITISH NEMERTEANS. 551 



vessels comranm'cate in the usual way with the median dorsal 

 vessel. Just in front of tlie caudal appendnge the median 

 dorsal vessel ends, while the lateral vessels form a ventral 

 commissure, from which arise two minute vessels. These soon 

 fuse, forming a cord of cells which is continued into the caudal 

 appendage. 



The excretory system consists of a duct on each side, 

 into which run a number of tuhules. The tubules lie in close 

 relation with the oesophagejil lacunae, and extend both dorsally 

 and ventrally to the level of the nervous side stems. After 

 the tubules come to an end the large duct is continued back- 

 wards, and opens by a single pore on either side just above the 

 side stems. It is remarkable that at least half the total ex- 

 tent of the excretory system is taken up by the lai'ge duct 

 unaccompanied by any excretory tubules. 



The gonads were in each case testes alternating with the 

 intestinal pouches. The ducts are much nearer to the median 

 dorsal line than to the side stems. No gonidial pouches are 

 found in the caudal appendage. 



The nervous system is formed on the usual Lineid type. 

 Of the four different kinds of ganglion cells enumerated by 

 Burger, all are present with the exception of the neurochord 

 cells. These are also absent from the side stems. The 

 cerebral organ is not very strongly developed. Its glandular 

 epithelium reaches forwards dorsally over the hinder part of 

 the dorsal ganglion (fig. 10). The epithelium of the ciliated 

 canal is not so highly differentiated as in the rest of the 

 members of the family in which it has been described. The 

 large and characteristic cells found on the external side of 

 canal are not present in Micrella, the whole canal being lined 

 by epithelium similar to that found on the inner side of the 

 ciliated canal of other Lineidee. The head slits are not deep, 

 extending only halfway to the brain. They end abruptly at 

 the level where the ciliated canal comes off. 



With regard to the other sense-organs, both eyes and 

 frontal organ are absent. There is, however, a lateral sense- 

 organ on either side (fig. 2) shortly behind the excretory pore. 



