42 EISEN 



The sperm-sacs are at first very narrow about as thick as the 

 dorsal vessel. They widen out in XIV, but even posteriorly do not 

 become wider than the intestine, or even as wide, and remain con- 

 fined to the ventral part of the ccelom. They originate from the tips 

 of the testes. 



Body-wall. Integument thick, especially the longitudinal muscular 

 layer. The pigment not continuously distributed, but found in small 

 patches, which latter are evenly distributed throughout the whole 

 length of the body. 



Nephridia (fig. ije). Not only is the outside form of the ne- 

 phridia characterized by a long anterior lobe, but the canals differ also 

 from those of Mesenchytraaids generally. Instead of being of even 



FIG. 17. Mesenchytrceus kincaidi. 



thickness throughout and closely wound, the canals are most irregular, 

 and furnished with a lumen which in places is very wide, and in other 

 places very narrow. In places even the lumen widens out to form 

 regular chambers. There is also a great deal of cellular matrix not 

 belonging to the ducts, and this matrix contains larger and smaller 

 vacuoles which probably stand in connection with the ducts. Near 

 the posterior lobe, where the returning duct connects with the narrow 

 duct leading to the pore, the return duct widens out more than any- 

 where else and its lumen forms a succession of chambers. These 

 chambers and widenings of the lumen are not exactly similar in the 

 various nephridia, but are subject to such variations that no two nephridia 

 are entirely alike. 



MESENCHYTR^US PENICILLUS sp. nov. 



pi. ix, figs, i and 2; text-figs. 18 and 19. 



Definition. Length 15 mm., width I mm. Somites 85. Pros- 

 tomium small and pointed. Setae : laterals, 4, 5, 6, 5, 4, 6, (XII) 



