165 



jects beyond the body wall. In the anterior region there are 4-6 

 (rarely 7 or 8) set?e per bundle; in the middle region, 4 setae (rarely 

 5) per bundle; and in the posterior region, 2-3 setae per bundle. 



INTERNAL CHARACTERS 



Brain. — The brain (PI. XI, Fig. 48) lies in the dorsal part of I 

 and II, chiefly in the latter. It is about twice as long as wide. The 

 posterior margin is broadly convex, while the anterior margin is 

 strongly so. The lateral margins are approximately straight and al- 

 most parallel, diverging only slightly caudad. In transverse section 

 the brain is elliptical in outline, its long diameter being approximately 

 twice as long as its shorter one. Two pairs of supporting strands arise 

 from its posterior part and extend obliquely across the coelom to unite 

 with the body wall. 



Peptonephridia. — The peptonephridia (PI. XI, Fig. 43) are simple 

 and unbranched. They arise from the digesti^'e tract in the anterior 

 part of V and extend caudad approximately parallel to it, encHng 

 in the posterior limit of V. The openings intO' the digestive tract 

 are latero-ventrad. Both peptonephridia are practically of the same 

 length and the free ends are usually closely approximated. In shape 

 these organs are cylindrical, sometimes slightly flattened. The maxi- 

 mum diameter is just caudad of the point of union with the digestive 

 tract, and from there the organs taper gradually to their free ex- 

 tremities. Slight irregularities on the surface produce a tuberculate 

 appearance, which, however, is not strikingly distinct. Sections show 

 these organs to be tubular, and conspicuous nuclei appear in the walls. 



Chylus Cells. — Chylus cells (PI. XI, Fig. 46) occur in the wall 

 of the intestine in a region including the caudal third of XIV and ex- 

 tending to the anterior part of XVII. In longitudinal sections this 

 region is very easily located by the abrupt increase in the thickness 

 of the intestinal walls. The cells are rather closely crowded, forming 

 an almost continuous layer. They are flask-shaped, somewhat trun- 

 cate at the ectal end, and the sides converge slightly entad. The in- 

 tracellular canal is distinct and its apical course is straight, but the 

 basal portion is bent at almost a right angle and is sometimes slightly 

 sinuous. The lining of the canal appears to be a very thin cytoplasmic 

 layer, but in many of the preparations it is rather difficult to dis- 

 tinguish it. Cilia are present for almost the entire length of the 

 canal. The perivisceral blood sinus is quite large in this region, trans- 

 verse sections of the worm showing it to be in contact with the 

 greater part of the surface of the cells. The ental epithelial cells are 

 more or less block-shaped, distinctly nucleated, heavily ciliated on 



