GENUS MONONCHUS (S.S.453)i5j 



Interplay of Organisms. There are regions where certain nematode 

 diseases of crops are very destructive, while other regions, the climate 

 and soil conditions of which are apparently similar, suffer but little, or at 

 least to a lesser degree, so far as we know. In such cases it is permis- 

 sible to suppose that the nematodes in the area where the lesser damage 

 is done are held in check by some as yet unknown agent. Is it not pos- 

 sible that the mononchs play some such role as this, and that just as cer- 

 tain insects hold other insects in check, so certain nemas hold other nemas 

 in check? 



We know relatively little about the life history of most of the mon- 

 onchs, and as yet very little about the possibility of controlling their 

 growth. One species, Mononchus longicaudatus, occurs at certain times 

 in almost inconceivable numbers in the sand of the slow filter beds of the 

 water works of cities. Near the end of the period of use the top layers 

 of the sand in these filter beds sometimes become in reality a huge culture 

 of this species. The observations suggest at least the possibility of culti- 

 vating this species on a large scale, should it prove desirable to do so. 



The discovery that the genus Mononchus is very large and to a con- 

 siderable extent composed of common and cosmopolitan species that feed 

 upon injurious plant-infesting organisms, suggests so many new lines of 

 research in soil biology as to make it desirable that a clear and connected 

 account of the members of the genus be available to investigators. This 

 need is increased by the fact that the literature is a scattered and frag- 

 mentary one, difficult to assemble. To these facts it must be added that 

 most of the new observations herein recorded have been made upon 

 species previously unknown. 



II 



GENUS MONONCHUS BASTIAN, 1866 



This genus is composed of non-marine, free-living nemas, with naked 

 cuticle and obscure amphids, and having a plain oesophagus preceded by 

 a broad that is, non-tubular pharynx, armed with 1 to 3 more or less 

 immobile teeth of which the dorsal is largest, and supplied with 6 power- 

 ful papillated lips. Ovaries reflexed, usually two. Testes two, out- 

 stretched ; spicula two, equal, simple, as are their small accessories ; there 

 is a pre-anal ventral row of supplementary organs. 



GENERA SIMILAR TO MONONCHUS, WITH DISTINGUISHING CHARACTERS 



Oncholaimns 



Anonchus 



Microlaimtts 



Irottus 



Nannonchus 



Oionchus 



Mononchtilus 



Marine; sometimes found in brackish soils. Has cephalic setse. 

 Has spiral amphids, and cephalic setse. 

 No thick muscular lips; amphids circular. 

 Pharynx tubular; teeth movable radially. 

 Has spiral amphids and cephalic setae. 

 Pharynx filled by single tooth, which is really spear-like. 

 Quite similar. Has much larger (ventral) spinneret; strongly developed 

 lateral fields; smaller pharynx; female organ single. 



