4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



In the collections of the parasitic species today there are no 

 more than 20 to 30 percent of new species. In the collections of 

 free-living forms from the fresh waters of Europe, this percentage 

 is even lower, but among the terricolous forms, Cobb (1917) de- 

 scribed as new 45 percent of his species of Mononchus, and Thorne 

 (1925) described as new 75 percent of his species of Acroheles. 

 This last figure is especially interesting as these are the results of 

 careful collecting in a very restricted area. Among the marine 

 nematodes in each large collection the new species are more numer- 

 ous than the described ones. Thus from the Black Sea the writer 

 found 80 percent of the species new ; from the Glacial Sea, in only 

 one of the best known orders, 70 percent. Steiner (1927) in the 

 Epsilonematinae found nearly 100 new species to add to the three 

 which were all those previously known. 



Furthermore, the parasitic species are known more or less over 

 the entire world. The free-living nonmarine forms have been most 

 fully studied in Europe, much less in North America and Australia, 

 and very little in the tropical countries. The marine forms also have 

 been systematically studied only in Europe, practically speaking. 



From the foregoing it seems probable that the free-living marine 

 species exceed in number, perhaps equal several times the number of, 

 both parasitic and fresh-water species, the two latter being nearly 

 equal in number of species. A comparison of the number of genera 

 would not give an adequate conception because of the lack of uni- 

 formity in the classifications of different workers. The parasitic 

 forms seem to be split up more than the free-living ones (cf. Bayhs, 

 1924). 



A second line of evidence as to the relations of free-living and 

 parasitic nematodes is in regard to their physiology. The marine 

 forms, probably with secondary exceptions among the few marine 

 Anguillulidae, are in free relations with the external world, the 

 water enters into their body through the cuticula, and probably the 

 ion concentration is the same outside the body as inside. If one puts 

 a marine nematode in a solution of some intravitam stain, for in- 

 stance, methylene blue, the first things to be colored are the granula- 

 tions of the skin and the peripheral nerve endings included therein. 

 Then the stain is concentrated in phagocytic cells, some muscles, 

 deeper-lying nerve cells, etc. In fresh-water forms the color pene- 

 trates through the cuticula more slowly, and penetrates chiefly 

 through the thin cuticula of the papillae, and through the mouth, 

 anal, and vaginal openings. In the intestinal parasites or in the 



