150< S -S.4S2) THE MONONCHS 



gether likely that these minute spermatozoa produced by mononch 

 syngones act in what would be called a normal manner, and as the sperma- 

 tozoa are known to do in other syngonic nemas in which they are of much 

 larger size, e. g. Rhabditis. 



Abundance; Distribution 



Frequency of Mononchs. Long ago Biitschli declared mononchs to 

 be among the commonest of nemas, an assertion that has been corrobo- 

 rated by all investigators in this field, hardly any of whom have failed to 

 note a number of species, occasionally new ones. Our knowledge of the 

 genus has been augmented in this way by de Man, Micoletzky, Ditlevsen, 

 Steiner, Hofmanner, Menzel, Daday, and the writer, until at the present 

 time about sixty species are known. Doubtless this number will be very 

 largely increased by future researches. 



Geographic Distribution. Variety of Habitat. Mononchs are found 

 in all the habitable regions of the world. They inhabit the soils and 

 fresh waters of every clime, occurring even at great depths in lakes and 

 at very high altitudes on mountains. While we have only just begun to 

 learn the details of their geographic distribution, it is already manifest 

 that some species are cosmopolitan. Several species occur both in Europe 

 and in North America, and a few of these same species are known also 

 from Australia. Considering the small number of observations hitherto 

 made along this line, it seems safe to predict that many of the species 

 will be found to be cosmopolitan. Some species adapt themselves to sur- 

 prisingly varied conditions. Mononchus longicaudatus, for instance, is 

 known from the tropics, from temperate regions, and from very cold 

 regions, and inhabits both soil and fresh water. Another species, Mon- 

 onchus brachyuris, is known both from warm springs and from cold 

 Alpine lakes. 



Abundance in Arable Soil. Mononchs occur in great numbers in 

 arable soil. On one occasion the writer estimated that at least thirty 

 millions of mononchs per acre were present in the top six inches of a 

 field of maize in New Jersey, and the actual number present may have 

 been much greater. They are regularly present in practically all arable 

 land of a sandy or loamy nature. 



The very numerous introductions of living plants into the United 

 States, through the agency of the Office of Seed and Plant Introduction 

 of the Department of Agriculture and other agencies, has brought about 

 simultaneously the introduction of many species of Mononchus. Nemas 

 existing in the soil about the roots of introduced plants are often 

 placed under favorable conditions for propagation in this country. It is 

 therefore certain that an unusual variety of mononchs exists in the soils 

 of the United States. 



