1899.] NATURAL SCIENCES OF PHILADELPHIA. 131 



•of the ampullse is of a character intermediate between that of the 

 stalk and the diverticula. 



As established by Eisen ('78) as a subgenus, Mesenchytrceus 

 included Enchytrseidse having sigmoid setae, a relatively short 

 sperm duct, and a supra-oesophageal ganglion which, while truncate 

 (straight or slightly convex) on the caudal margin, is deeply cleft 

 cephalad; besides these characters certain peculiarities of the 

 spermatozoa were mentioned. Michaelsen's studies ('88") on M. 

 setosus and other species have led him to add two very important 

 and, among the Enchytrseidse, unique characters, viz., the presence 

 of sejDtal sperm sacs and ovisacs, and of lobate nephridia, in which 

 the Ciosely folded tubule can be traced as such. All described 

 species of Mesenchytrceiis, which, following the usage of Michael- 

 sen, is now ranked as a full genus, agree also in the possession of 

 the following characters, in respect to which the genera of Enchy- 

 trseidse differ among themselves. The setse are sigmoid and are 

 asymmetrically arranged in the bundles, of which the ventral con- 

 tain (at least anteriorly) a greater number of setse than the dorsal. 

 Dorsal pores are absent, but a large head-pore is situated near the 

 apex of the prostomium. The dorsal blood vessel arises within^ or 

 caudad to the clitellum and contains a cellular heart-body. The 

 blood is colorless. Salivary glands are absent. The supra- 

 oesophageal ganglion is broader than long, deeply cleft anteriorly 

 and straight or slightly convex posteriorly. The nephridia have 

 very small anteseptal portions consisting of the funnel only, and 

 large irregular massive postseptal portions. The sperm-duct is not 

 more than ten times (Michaelsen says eight times) as long as the 

 funnel. This statement of characters is derived mainly from 

 Michaelsen's Synopsis ('89). 



The " snow-worm " described above, presents all of these char- 

 acters with the exception of the relatively short sperm ducts, which 

 are about fifteen times as long as the funnels. The slight modifi- 

 cation of the generic definition made necessary to receive this species 

 is, however, unimportant, in view of the considerable variability 

 in the length of this organ exhibited by species already known. 

 In M. fenesfratus Eisen ('78), the ducts but just equal the funnel 

 in length, in M. falciform is Eisen they are six times and in 3L 



^ In an undescribed species from the neighborhood of Philadelphia. 



