TWO AQUATIC OLIGOCH.32TES. 41 



and one slender prostomial nerves ; the lateral lines branch out 

 from the lateral prostomial nerves, while the median nerve leads 

 to the prostomial ganglion, which is nearly twice as large as in 

 L. gotoi. 



The peripharyngeal commissures commence at the posterior 

 corners of the lateral prostomial nerves and unite with the first 

 ventral or subpharyngeal ganglion in segment II. 



In the ventral nerve cord, the median neural canal begins 

 in the middle of segment IV and the two lateral canals in seg- 

 ment V ; they always lie side by side close to the dorsal border 

 of the cord, with the middle one in the median line. The 

 median canal is absent in the most posterior segments. 



7. Genital system. 



1). Testes. One pair of testes are attached to the posterior 

 face of septum IX/X, close to the ventral nerve cord. Each testis 

 is pear-shaped and is enclosed in a very thin membrane which 

 is open at the dorso-posterior side. 



2). Sperm- sacs. In the present species both the anterior 

 and the posterior sperm- sacs are unpaired. The anterior one, 

 lying in segment IX, is an anteriorly directed outgrowth of the 

 anterior septum of segment X, and lies on the dorsal side of the 

 intestine. It is kidney- shaped and large and contains numerous 

 sperm cells in different stages of development. The posterior one 

 is a posteriorly directed evagination of the posterior septum of 

 segment X and is confined to segment XI. It lies on the dorsal 

 side of the intestine, although its blind end sometimes tends to 

 lie more ventrally, and is less well developed than the anterior 

 sperm-sac. The sacs have the same structure as in L. gotoi. 



In L. gotoi, only small numbers of sperm cells are present 

 in the ccelomic cavity of segment X, but in this species, they 

 are very numerous and richly supplied with cœlomic vessels. 



3). Sperm- ducts. These lie in segment XI. 



a. Funnel. It is very wide and attached to the anterior 

 face of septum X/XI, on each side of the ventral median line. 



