45 2 
WORMS. 
worm reaching a length of nearly one quarter of an inch. Its shape is unusual, 
on account of the presence of a hump projecting like an excrescence from the 
surface of the abdomen, some distance 
from the tail-end. When fully formed, 
this excrescence amounts in size to half 
the length of the entire worm, and contains 
the young, which, after making their 
escape, undergo a short development in the 
body-cavity of the midge, then reach the 
outside, where they are transformed into 
mature males and females. After the 
pairing of the sexes, the males perish, 
but the females again enter the larva and 
start another cycle of metamorphosis. 
The second kind (Sphcerularia bombi), 
which infests humble-bees, closely re¬ 
sembles the first in development; but the 
excrescence, or brood-pouch, of the mother- 
worm is changed into a tube, and ultim¬ 
ately reaches a size from fifteen to twenty 
thousand times as great as the parent, 
which dwindles in size in proportion as 
the sac grows. The life-history of this 
worm is shown in the illustration, where 
A is the free-living male, B represents the 
free-living female, and C is the parasitic 
female ( w ), with her brood-pouch. 
Of the thread-worms infesting the 
human body, one of the commonest is 
Ascaris lumbricoides, which is found in 
numbers varying from one or two only 
to over two thousand. These worms 
usually infest the small intestine, but 
sometimes enter the stomach, or even 
penetrate into the liver. Large examples 
reach a length of 6 inches or more, and 
the females produce about sixty millions 
of eggs annually. These are naturally 
dispersed abroad everywhere, and as the 
young worm retains its power of growth 
in spite of frost, drought, and, in fact, the 
HUMBLE-BEE THREAD-WORM. 
A, Male enlarged : a, nat. size. 
B, Female enlarged ; b, nat. size. 
O, Brood-pouch of female (w ); c, nat. size. 
most unfavourable circumstances imagin¬ 
able, and is, moreover, far too small to be noticed, we need not feel surprised at 
the prevalence ol the pest. The form and some of the structural characters of 
this worm are shown in the two illustrations on p. 453. In the uppermost, 1 is 
the male, and 2 the female, of the natural size, 3 being the egg, enormously 
