922 
Journal of Agricultural Research 
Vol. XXIII, No. II 
SOURCES AND DETERMINATION OF THE NEMAS 
In the main the material for these investigations was collected at Falls 
Church, Va., but questionnaires were sent to zoologists all over the United 
States. Nearly 160 of these were returned, some with collected Mer- 
mithid material, and many with very interesting information about dis¬ 
tribution, hosts, etc. 
The examination of this contributed material is not yet finished, and 
therefore no more than a somewhat brief sketch of the American Mer- 
mithid land-fauna can be given, together with some aspects of the eco¬ 
nomic value of the family. 
On leaving the insect host the nemas enter the soil. There have been 
observed thus far a dozen or more species of Mermithids from American 
soil, mostly new. The two most common are what have been called 
Mermis albicans Von Siebold and M. nigrescens Dujardin, which are among 
the first Mermithids made known and also the ones most frequently men¬ 
tioned in literature. Both apparently have a wide geographical distribu¬ 
tion. 
The determination of Mermithid species is difficult; one reason is 
that often only larval forms are obtainable, and another is that Mer¬ 
mithids do not possess obvious morphological characteristics. The 
present studies were much aided by the excellent papers of Meissner 
(5, 6) 2 Rauther (7), and Hagmeier (3). The latter emphasized the 
opinion that among the principal and best aids in classifying Mermithids 
are the sense organs on the head, since they rarely change during the life 
of the individual. 
Whereas Mermis nigrescens seems to show little variation and to be 
represented in this country by the typical European form, the American 
Agamermis decaudata is unusually difficult of determination, even for a 
Mermithid, because it presents an extensive series of variations, between 
the extremes of which there is a complete gradation of intermediate 
forms. These varieties, or races, and apparent hybrids are best 
recognized by the structure and arrangement of the head sense organs. 
As far as can be judged, the European albicans as described by Meissner 
(5, 6), Rauther (7), and Hagmeier (3) has not yet been found in this 
country. The chaos of these forms is probably greatly augmented by 
hybridization. Cases occurred at Falls Church where the mating female 
and four males (four males with one female) all differed in the structure 
of the head sense organs. 
Another interesting evidence of the existence of a number of different 
races in Agamermis decaudata is the fact that almost any collection that 
includes a number of female specimens will show intersexes—that is, 
females with more or less well developed male sexual organs. Experi¬ 
mental biology is showing that such intersexes may be frequent in the 
“artificial” crosses of closely related forms, races, or genotypes. A. 
decaudata as it occurs in nature, is not a clean-cut species, but rather a 
mixture of races and their hybrids. 
The origin of the races of Agamermis decaudata is still uncertain. 
Perhaps the great variety of hosts may have some influence. 
It may be considered questionable whether there are decaudata races 
special to certain hosts. We do not know yet, but it appears as if larvae 
of various races are entering hosts without special choice. 
* Reference is made by number (italic *to “ Literature cited,” p. 926. 
