KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 15. NIO 7. 43 



EXPL A NATION OF THE FIGURES. 



PLATE I. 



Fig. 1. Mesenchytrmus primcevus n. sp. 



a = the worm, nat. size. 



b = the front part seen from the side. 



c = the hind part also seen from the side. 



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



/ = the front part of the nervous system, seen from above. The deep eraargination of the postcrior 

 margin of the supra-oesophagial ganglion, as drawn here, is abnormal and existed only in one specimen. 



g = the same ganglion of an other specimen, seen from below. 



h = the receptacle in the fourth segment behirid the segmentum buccale. 



k = the efferent duct filled with spermatozoa, which are also seen penetrating dovviv the tube, towards 

 the copulative organ. The duct is seen from the side and presents a very regular flasklike shapc. 



m = the same organ seen from the front. The tube is not represented. 



o = one of the ovaries with a ripe egg at the top. 



p = another ovary not ruueh developed, all the eggs being of the same size. 



q = another ovary with two developed eggs in the middle, surrounded at the ends by unripe eggs. 



r = another ovary with a developing egg at the top. 



s = a few of the perigastric bodies. 



t = curious globules containing a fatty substance; found in great numbers in the perigastric cavity of 

 the body. 



Fig. 2. Mesenchytrmus falciformis n. sp. 



a = the worm nat. size. 



b = the front part seen from above. The numbers indicate the number of the segments. The segments 

 not numbered are: the first: lobus cephalicus and the second: segmentum buccale. 



c = the hind part from above. 



d = the front part of the nervous system from above. The front part of the ventral cord is very much 

 swelled and emittiug a small nerve towards the mouth of the worm. 



e = the receptacle, at the top of which is a slight swelling containing the spermatozoa. 



/ = one of the ovaries showing two ripe eggs at the top. 



g = sotne of the perigastric cells. 



h •— the efferent duct filled with encysted spermatozoa. At the lower end of the vesicle is a helix-like 

 organ not found in any other species. This organ is not ahvays of so regular a form as represented on the 

 figure. 



PLATE II. 



Fig. 3. Mesenchytrmus mirabilis n. sp. 



a = the worm, nat. size. 



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



c = the receptacle duplicated abuormously. The left one is seen in optical section. 



d= a normal receptacle from another specimen. 



e = the efferent duct with an extraordinarily short tube. 



/=the same duct from another individual, surrounded at the lower end or orifice by numcrous ovaries 

 in a not very advanced state of development. 



g = the lower end of the efferent duct and the organ of copulation, surrounded by several ovanes. The 

 ovaries in front of the duct are not represented. 



