12 GUSTAF EIS EN, ON THE AUCTIC OLIGOCHiETA 



1. Mesenchytranis primaevus n. 

 Pl. I. Fig. 1. 



The supra-cesophagial ganglion rectangular, and broader than long, tlie two 

 lobes being deeply divided in front (fig. 1. f and g). 



The receptacle is unusually minute, furnished in the middle with a lobated swel- 

 ling for the reception of the spermatozoa (fig. 1. h). 



The efferent duct is bottle-shaped, the tube being hardly longer than the vesicle 

 (fig. 1. k). 



The segmental organs have three very large middle lobes. The onter duct is short, 

 the inner one is of the length of the middle lobes (tig. 24). 



The testes are in the 9 th and 10 th segments (fig. 42). 



The ovaries in the ll th and 12 th segments (fig. 42). 



The segments are about 52 and well defined. 



The length. of the body about 10 m. m. 



The width » » » » l 1 /- m. in. 



The spines are of equal length and slightly curved in each of the segments 5, 7, 1 ) 7, 5. 



Habitat. This species is distributed över a very wide area, being found from 

 Novaja Semlia down to the 62 th lat. along the shores of the Jenissej. The localities on 

 which they were found are the following: Matotschkin 73° 25'; Möller bay 72° 25'; 

 Krestowskoj 72° 15'; Melnitschnij 65° 17; Intsarevo 62°. 



The most remarkable character of this species is, without any doubt, the minute- 

 ness of the receptacle. It is at least ten times smaller than that of any other species, 

 and so tender and of so fine a structure that it can be dissected only with the grea- 

 test precaution, and in fact, with all the specimens I used for dissection I succeeded 

 but once to get a good preparation of this very minute organ. 



Thus when separating the species of the collection it was always the first sign 

 of having the present species before me, that I could find nothing in the fourth seg- 

 ment, where I knew that the receptacle must be found. 



In all other respects the specimens were fully developed, and I doubt if a further 

 advanced maturity would bring the receptacle to a higher stage of development. It 

 is true I never found any spermatozoa in its lobes, but otherwise that is no sign why 

 that organ should not be fully developed. 



Apart from the minuteness of the receptacle the efferent duct also offers a 

 strong contrast compared with the same organ of any other species of Enehytrceus 

 known to me. In other species we are accustomed to find the said vesicle furnished with 

 an extremely long and narrow tube, rolled in innumerable winclings. But in our pre- 

 sent species and in its allied companion Eneliytrceus mirabilis the said tube is very 

 short and wide and especially in Mes. primcevus not longer than the vesicle itself. 



') 3 indioates that the number of the spines in each bundle is decreasing towards the front and the hind 

 part of the worm. 



