coe: nemerteans of west and northwest coasts. 33 



The circular muscles are as a rule much thinner than the longi- 

 tudinal layer or layers (PI. 12, fig. 80), and in some forms (as 

 Cephalothrix) are but little developed. In most of the Lineidae 

 the circular muscular layer sends off strands of fibers dorsally and 

 ventrally, which pass obliquely through the outer longitudinal mus- 

 cles to form a very thin outer layer of circular fibers immediately 

 beneath the outer endothelium. In doing this the strands fi-om the 

 right side cross those fi'om the left in the midst of the longitudinal 

 muscles to form the characteristic dorsal and ventral muscular crosses. 

 These are situated at an angle of 90° with the pair of nerves. 



In these orders the proboscis is provided with a single pair of 

 nerves situated right and left (PI. 12, fig. 80) in a position corre- 

 sponding to that of the lateral nerves of the body. They lie directly 

 beneath the inner epithelium except in such of the Lineidae as have 

 an inner longitudinal muscular layer, in which case they are situated 

 just outside this layer. They always branch profusely, and in the 

 Lineidae form so complete a ])lexus that the two main nerve cords 

 are not to be recognized except in the anterior portion of their course. 



The outer surface of the muscular layers is covered by a thin layer 

 of flattened endothelial cells which are bathed in the fluid of the 

 I'hynchocoel and rest upon a delicate basement layer (PI. 11, figs. 66- 

 71), while the inner surface of the muscles supports a very thick and 

 highly specialized epithelium. The anterior portion of the proboscis 

 in Carixomella (PI. 11, fig. 67) is provided with a very thick base- 

 ment layer, which farther back assumes a position between the longi- 

 tudinal and the circiilar musculatures (PI. 11, fig. 67), as described 

 in the account of the species. 



This epithelium consists almost wholly of various kinds of gland 

 cells (PI. 11, figs. 66, 67) from which mucus and other very viscid 

 fluids are secreted, as well as various kinds of rhabdites (PI. 11, fig. 

 72), and, in many Lineidae, urticating filaments. It is thrown up 

 into prominent pa{)illae covered with high pvi'amidal cells. A 

 description of these cells and of the rhabdites occurs in the specific 

 discussion of Carinomella lactea. 



When urticating cells are present each cell contains a number of 

 capsules each with a coiled urticating filament several times as long 

 as the capsule itself. Such cells often occur in two longitudinal 

 bands on opposite sides of the proboscis. The extremely viscid 

 secretion of certain of the cells excellently serves the purpose of 

 grasping prey. 



