14 GUSTAF EISEN, ON THE ARCTIC OLIGOCHJETA. 



acute and the middle part of the receptacle segraented (Pl. II. fig. 3. d). In one spe- 

 cimen I fonnd on one side two receptacles united with their tubes near the exteriör 

 porns. On the other side of the same segment there existed only one receptacle as 

 usual (Pl. II. fig. 3. c). 



The tube of the receptacle is very short, only in one specimen attaining the length 

 of '/a or Va 0I " the whole organ. 



The efferent duct. In two of the specimens the tube was rather long and at 

 least six or eight times as long as the vesicle. In the other specimen on the contrar} 7 

 the tube reached not a fourth of that length; I consider this abnormal. The shape 

 of the vesicle in all the three specimens was about the same, somewhat irregular. On 

 the top of the vesicle is an impression or cavity, which, however, does not form the 

 entrance for the spermatozoa. 



One of the specimens had three efferent ducts in the same segment, or two on 

 one side and one on the other. But it was not the specimen which had the duplica- 

 tion of the receptacle. Whether and in what manner the efferent ducts were united I 

 could not ascertain. 



The ovaries were always found surrounding the base of the efferent duct, but 

 perhaps always affixed to the epithel of the body wall. 



The location and number of the testes were, as stated, not alike in any two of 

 the dissected specimens. Besides, those organs were of two kinds, one lobed, situated 

 in the ll th and 12 th segments, the other, not lobed, in the other segments. 



The perigastric bodies also varied to some extent, the nucleus being sometimes 

 invisible, sometimes eccentric, and the shape of the body varying from circular to oval 

 or irregular as best shown by the figures (fig. 3. t). Altogether the variation of the 

 principal organs of this species is quite wonderful and exceptional, especially as nothing 

 of the kind has been found in closely allied species or, in fact, in any other species 

 of the genus Enchytrasus. 



3. Mesencliytraeus falciformis n. sp. 



Pl. I. Fig. 2. 



The supra-cesophagial ganglion is nearly square or rectangular with the largest 

 diameter in the direction of the length of the body (fig. 2. d). 



The receptacle consists of a simple tube without follicles or enlargement for the 

 spermatozoa, but somewhat differentiated near the base, being surrounded there by a 

 longitudinal layer of fibrillaB (fig. 2. e). 



The efferent duct has a tube about six times longer than the vesicle, and the 

 latter is furnished at the base with a very characteristic screwlike, twisted swelling just 

 between the vesicle and the narrow tube (fig. 2. h). 



The segmental organs are considerably smaller than those of the preceding spe- 

 cies and have a larger middle lobe and an outer and inner duct comparatively short, 

 (%• 26). 



