44 GUSTAF EISEN, ON THE ARCTIC OLIGOCHiETA. 



h = one of the testidés containing ripe spermatozoa encysted in small round bags, wliich do -not burst 

 before eiitering the vesicle of the efferent duct. 



k = one of the cysts containing four separate bundles of spermatozoa. 

 m = another eyst of a different shape. 



o = the same cyst showing the outside. Membrane dotted with small warts. 



p = one of the ovaries with unusually small lobes and eggs in different stages of development. 



q = the top of one of said lobes with further developed eggs. 



r = the top of another lobe, the eggs are here not so far developed. 



s = the top of another lobe, with eggs more advanced in development. 



t = differently shaped perigastric cells, some having a nucleus which can be seen plainer than in others. 



PLATE III. 



Fig. 3. Mesenchytrceus mirabilis n. sp. 

 u = A normal receptacle with the top bent över, and unusually long. 



Fig. 4. Archienchytrceus Levinseni n. sp. 

 a = the worm, nat. size. 

 b = the front part seen from the side. 

 c = the hind part seen from the side. 



d = a bundle of spines, showing their relation size and form. 

 e = the front part of the nervous system. 



/ = the reoeptacle, at the top of which is a swelling containing spermatozoa. 

 g = the efferent duct; the vesicle is seen in optical section. 



h = a curious layer of a vitreous substance, found in each segment all round the body wall; perhaps ho- 

 mologous with the perigastric cells of other species. 



Fig. 5. Archienchytrceus tenellus n. sp. 

 a = the worm, nat. size. 



b = the front part of the worm seen from the side. 

 c = the posterior part of the worm seen from above. 

 d = a bundle of spines showing their relative length and number. 

 e = a part of the epidermis showing the fenestration. 

 /=the front part of the nervous system seen from above. 

 g = a receptacle, near to the orifioe furnished with some small glands. 

 h = the efferent duct and the penis. 

 k = several perigastric cells. 



PLATE IV. 



Fig. 5. Archienchytrceus tenellus f. elongatus n. f. 



m = the receptacle, elongated and bent at the top. 

 o = the supra-cesophagial ganglion seen from above. 



Fig. 6. Archienchytrceus lampas n. sp. 

 a = the worm, nat. size. 



b = the supra-cesophagial ganglion seen from above. 



c = the receptacle, showing the sack-like enlargement of the top, a bundle of spermatozoa just enter- 

 ing the vesicle. 



d = the efferent duct. 



e = perigastric cells; one is seen from the front, the other from the side. 



Fig. 7. Archienchytrceus Dicksoni n. sp. 

 a = the worm, nat. size. 



b = the front part of the worm, showing the two largest segments, lobus cephalicus and segmentum 

 buccale. 



