COE: NEMERTEANS OF WEST AND NORTHWEST COASTS. 291 



Fig. 58. — Tet.rastemma ni- 

 (/rifrons. Central stylets 

 and Ijases, showing more 

 opacjue posterior portions. 



being often less than one third as wide as head. The marking is 

 acutely triangular, with its pointed apex in the 

 median line anteriorly. Body pale brownish, 

 buff, deep flesh color, or occasionally whitish 

 with a faint tinge of brown. A paler, or 

 whitish, line often extends longitudinally on 

 dorsal surface to posterior end of body ; ven- 

 tral surface pale buff or grayish throughout. 

 The red blood vessels are naturally more con- 

 spicuous than in the darker varieties. 



Othei; varieties are reddish brown, thickly 

 sprinkled with minute dots of darker color on 

 dorsal surface ; ventral side of head white, 

 with white median band extending posteri- 

 orly as far as intestinal region ; rest of ven- 

 tral surface reddish brown. Other specimens 

 are brick red in esophageal region and chest- 

 nut brown posteriorly, with ventral surface 



grayish or pale reddish. In fact, there are all possible gradations 



between the most extreme 

 color vaiieties, but all agree 

 in having the cephalic mark- 

 ing dark l)ro\vn in color. 



Pigment to which color 

 of body is due resides in in- 

 tegument, except that of the 

 cephalic marking, which is 

 placed deep among tissues 

 of the head. Integument 

 and pigment often sloughed 

 off before death, leaving the 

 body pinkish or flesh color, 

 with the ocelli and red. blood 

 vessels showing very conspic- 

 uously. 



General color of hodj is 

 retained after preservation, 

 and the cephalic marking is 



Fig. 59.— Tetrastemma nigrifrons. Outlines of 

 accessory and central stylets and bases, show- 

 ing variations in form and size, x 240. 



[)erfectly distinct even after imbedding in paraffin. 



