45 6 
WORMS. 
curiously shaped; the body being cylindrical, and consisting of a thick fore-part, 
and a thinner tail-like appendage. Out of the front end of the body a sort of head 
can be thrust, which is armed with two circles of small hooks, and tipped with a 
horny proboscis. With these instruments the creatures, in the first place, bore their 
way through the egg-shell, and, having made their escape, lie quietly at the bottom 
of the water without appearing to wander in search of a host. Insects, how¬ 
ever, in the adult and larval stage abound in most fresh waters, and sooner or later 
the young worms come 
across them. They then 
seek out a soft spot, bore a 
hole by their apparatus of 
hooks, and by a series of 
contractions and extensions 
of the body force an entrance 
between the muscle-fibres 
of the limb, whence they 
spread into the body-cavity 
of their host. In the illus¬ 
tration, a and b show two 
views of the larva with its 
armature of hooks, and c 
represents two that have 
effected an entrance into the foot of the larva of a May-fly. They also infest in this 
way water-bugs and gnats. All these water-insects, however, are liable to be devoured 
by fresh-water fish, and by this means the young hair-worms are set free in the 
intestines of the fish, where they undergo their 
metamorphosis, and after five or six months pass 
into the water in the mature form. Nearly allied 
is the family Mermithidcc, containing the genus 
Mermis. Like the hair-worms, they occur both 
singly or coiled up and entwined with each other. 
The eggs are curiously constructed, having the 
form of lenticular capsules, with a pair of tassel¬ 
shaped appendages projecting from their flat sur¬ 
faces. Eggs of M. albicans laid in the summer do EGGS AND LARVA 0P Mermis (enlarged) . 
not hatch until the spring. After remaining a 
short time in the earth, the young search for insects and larvae, bore a way into 
their bodies, where they gradually grow to maturity, and ultimately pass out to 
lead a free life, when they pair and lay their eggs. They may be found in cater¬ 
pillars, grasshoppers, and more rarely spiders. 
LARViE op Gordius — a, showing proboscis, and b, circlets of hooks on the 
head ; c, two examples lodged in the foot of a larva of the May-flv. 
Arrow-Worms, —Order Ciretognatha. 
The small group of worms included under this heading are of doubtful position. 
They are glass-like, transparent creatures living in the sea, near the surface of 
which they swim in numbers. They are most active and vigorous swimmers, as 
