ENCHYTR^EID^E 13 



with minute anteseptal. Setae sigmoid or straight. Rudimentary 

 peptonephridia 9. Bryodrilus Ude. 



Dorsal vessel rises from a sinus in VIII, formed by the junction of 

 esophagus and intestine, which suddenly merge into each other. 

 Intestine with two to four intestinal pouches or with none. Large 

 peptonephridia. Setae sigmoid or straight. 



10. Henlea Michaelsen. 



C. Setae straight, the inner ones always shorter than the outer ones. 

 Dorsal vessel rises posterior to clitellum. Blood colorless. In- 

 testine without pouches. Two kinds of lymphocytes. Dorsal 

 pores in the dorsal median line half way between the septa. 



Four fascicles of setae. Dorsal pores begin with VI or VII. 

 Chylus cells in some somites in the vicinity of clitellum. No 

 cardiac gland. Peptonephridia simple or branched. 



ii. Fridericia Michaelsen. 



Only the ventral fascicles of setae present, anteriorly 4 setae, posteriorly 

 rarely more than one seta in each fascicle. A cardiac gland. 

 Dorsal vessel post-clitellial. Some of the anterior septa are 



thickened 12. Distichopus Leidy. 



JD. Six fan-shaped fascicles of setae in each somite. Two fascicles 

 are ventral, two lateral and two subdorsal. The setae in the ven- 

 tral and lateral fascicles four to nine, simple, acute, curved like 

 an italic f\ those of the dorsal fascicles stouter and less curved, 

 three to six in each fascicle. Blood colorless. 



13. Chirodrilus Verrill. 



SYSTEMATIC DISCUSSION OF GENERA AND SPECIES. 

 Subfamily MESENCHTTRsEINJE. 



This subfamily includes for the present only the single genus, after 

 which the subfamily takes its name. In his arrangement of the family 

 Michaelsen places Stercutus close to Mesenchytrtzus on account of 

 the sigmoid setae. It seems to me, however, more probable that this 

 genus is more closely related to Pachydrilinae on account of the form 

 of its nephridia. The structure of the penial bulb of Stercutus is not 

 known to me. 



The penial bulb is in some species of Mesenchytrceus rather reduced 

 in size as well as variable in structure, but all the species agree in hav- 

 ing the lower part of the sperm-duct invested by muscles, which in 

 some instances are of most powerful nature, reminding us of the mus- 



