278 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



posterior extension of the anterior marginal groups, there sometimes 

 appears a posterior group which apparently extends posteriorly and 

 inwardly (PL 23, fig. 162) instead of laterally as in the individuals 

 with fewer ocelli (fig. 163). Sometimes, also, the arrangement into 

 definite groups is not apparent, and the ocelli appear to be scattered 

 irregularly along the lateral margins, with irregular longitudinal 

 clusters nearer the median line. 



Proboscis. — Proboscis sheath extends to posterior end of body. 

 Proboscis of large size, and about as long as the entire worm ; 

 whitish, pale yellowish or slightly rosy in color. Usually provided 

 with 10 nerves, although 11 are present occasionally. Central sty- 

 let slender and acutely pointed. Basis conical or bell-shaped ; usu- 

 ally much wider at its posterior border than more anteriorly (PI. 16, 

 fig. 98; PL 23, figs. 165-168, 170, 171). As a rule, the smaller 

 individuals with fewer ocelli have the basis much more widened and 

 bell-shaped posteriorly than do the larger individuals with more 

 numerous ocelli. Thus the proboscis of the individual figured on 

 PL 16, fig. 98, has a wide, bell-shaped basis, while a larger individual 

 with more than double the number of ocelli (PL 23, fig. 165) has a 

 more slender, conical basis. 



Basis is of just about same length as the slender central stylet, or 

 a little shorter, and is from one half to three fourths as wide poste- 

 riorly as its length. Length of largest basis measured was fully 

 double that of smallest ; measurements of a large number of bases 

 ranging from .044 to .09 mm. in length and .025 to .042 mm. in 

 width. 



These variations in the stylet apparatus of proboscis, when taken 

 with the decided variation in color of body and number of ocelli, 

 suggest that several species may be represented, and this was my 

 impression for a long time. Careful comparison of a large number 

 of individuals, however, convinced me that it was absolutely impos- 

 sible to draw a sharp line of demarcation between any two groups 

 of individuals that would agree both in regard to the ocelli and the 

 proboscis armature. It seems necessary, therefore, to unite all these 

 forms into a single, variable species. 



Proboscis sheath corpuscles are conspicuous under high magnifica- 

 tion because of their pale yellowish color. 



Cephalic glands well developed ; submuscular glands practically 

 wanting. 



