LINEUS. 255 



spherical nuclei (PI. III., fig. 5). It is sparingly provided 

 with long cilia. Near the blind end of a tubule these 

 cilia are often more abundant, and are directed away from 

 the blind end (PI. III., fig. 5). No flame cells, however, 

 have been detected in this species. 



The excretory system lies almost wholly above the 

 level of the lateral nerve cords, never extending into the 

 lacunar network ventrally. Though it is in close con- 

 tact with the oesophageal lacunae, there is no communica- 

 tion between the vascular and excretory systems. 

 Although certain observers claim to have demonstrated 

 such a communication for certain of the more primitive 

 forms, such as Carinella and Carinoma, it is exceedingly 

 doubtful whether it exists. Concerning the nature of the 

 fluid contained in the excretory system no observations 

 have been made. 



NERVOUS SYSTEM. 



The nervous s} r stem consists essentially of two longitu- 

 dinal cords extending throughout almost the entire length 

 of the body and dilating anteriorly into the brain. Pos- 

 teriorly they unite by a fine commissure ventral to the 

 rectum. For their whole course they lie immediately 

 outside the circular muscle layer, and are conspicuous 

 objects in a transverse section of the worm (PI. III., fig. 8, 

 ss.). Viewed thus they are seen to be composed of an 

 inner granular-looking portion of a more or less circular 

 outline, surrounded by a layer of ganglion cells. The 

 latter are not present on the side next to the circular 

 muscles, and are very scarce externally. The fibrous core 

 is bounded b} r a thin connective tissue layer, the inner 

 neurilemma, separating it from the ganglion cells. Out- 

 side the ganglion cells is another connective tissue layer, 

 which has been termed the outer neurilemma. The inner 



