314 Jo G. i>T5 Man : Aquatic animals from Tibet. [Voi,. II, 



NOTE ON A FREE-LIVING NEMATODE FROM 

 RHAM-TSO LAKE, TIBET. 



By Dr. J. G. de Man, lerseke, Zeeland. 



The single specimen of free-living Nematode which was collected 

 by Captain F. H. Stewart in Rham-Tso Lake, Tibet, belongs to a 

 long-tailed species of the genus Dorylaimus , Duj., and is apparently 

 most closely related to the well-known D. stagnalis, Duj., of the 

 fresh water of Europe. The point of the partly protruded spear is 

 broken off, as also the extremity of the tail. 



The measurements of this specimen, which is an egg-bearing 

 female 5*45 mm. long, are the following : — 



Length of oesophagus . . . . i'04 mm. 

 Distance between posterior extremity of the 



oesophagus and the genital aperture . . i'33 ,, 



Distance between genital aperture and anus 2"83 ,, 



Length of the tail .. .. .. 0*24 ,, 



Length of the body .. .. 5*44 ,, 



Breadth at base of head .. .. 0'023 ,, 



Breadth at posterior extremity of oesophagus 0*126 ,, 



Breadth at the genital aperture .. 0'i33 ,, 



Breadth at the anal aperture . . . . 0*063 ,, 



Length of the anterior [i.e., antevaginal) part 



of the genital organs . . . . 0*94 ,, 

 Length of the posterior [i.e. , postvaginal) part 



of the genital organs . . . , 0*94 ,, 

 Proportion between the length of body and 



the average breadth . . , . ^- 

 Proportion between the length of body and 



that of oesophagus , . . . f 

 Proportion between the length of body and 



that of tail . . . . . . Y- 



These measurements fully agree with those of D. stagnalis, 

 Duj. {vide de Man^ " Contribution a la connaissance des Nematodes 

 libres de la Seine et des environs de Paris," Annates de Biologie 

 lacustre, ii, 1907, p. 25, pis. ii and iii, fig. 5). Both species fully 

 resemble one another as regards the general shape of the body and 

 of the oesophagus, the structure of the head or cephalic region, the 

 situation of the genital aperture and the shape of the tail. In one 

 character, however, this specimen differs from D. stagnalis. On 

 behalf of the quoted paper on the free-living Nematodes of the river 

 Seine, no less than twelve female specimens of D. stagnalis were 

 measured by me, for the greater part, if not all, egg-bearing ; in all 

 these specimens the posterior part of the genital apparatus proved 

 to be distinctly longer than the anterior, i.e., that part which is 

 situated between the genital aperture and the oesophagus ; the 

 posterior part, indeed, appeared li to 1^ times, in one individual 



