THREAD- WORMS. 
45 1 
If they fall in with one, they start to creep up it, and mounting ever higher and 
higher, as the corn grows, ultimately succeed in reaching the summit. They then 
attack the soft 
bore into 
gram, Dore 
it, and form gall¬ 
like swellings, in 
the middle of each 
of which there is 
a larval worm. 
Here the worms 
quickly develop to 
normal perfection, 
and after the 
females have laid 
a large quantity of 
eggs, both they and 
the males die. 
Subsequently the 
eggs hatch, and the larvae, which constitute the powdery substance referred to 
above, make their appearance. Somewhat similar diseases are produced in other 
grains by members of the same family; and the turnip-eel (Heterodera) is very 
destructive to root-crops. 
Of the parasitic forms, the genus Hhabdonema has a remarkable course of 
vinegar-eel (much enlarged). 
development, one species ( R. nigrovenosum), which is about three-quarters of an 
a, female of Rhdbditis —form of Rhabdonema nigrovenosum ; b, brood-pouch. (Enlarged.) 
inch in length, living, sometimes in great numbers, in the lungs of frogs. This 
species is hermaphroditic, and produces innumerable young ones, which bore their 
way from the lungs into the alimentary canal of their host, whence they are 
expelled with the remains of their food. They then develop in a few days into 
free-living, separately-sexed individuals, bearing a close resemblance to another 
free-living worm ( Rhabditis ). These individuals breed; the females bear one 
or two young apiece, and these, after devouring their mother’s vitals, and making 
their escape by bursting through the skin of her body, pass through a frog’s mouth 
into its lungs, and become the hermaphrodite adult. Another species (R. strongy - 
loides ) is of interest, inasmuch as it is parasitic in man in warm climates. 
Two more remarkable Nematoids may be mentioned, both of which infest 
insects. The first of these, Atractonema gibbosum, is found in numbers in the 
body-cavity of the larval and adult stages of the midge; the completely-formed 
