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 



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j.a.rv;e of 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-fly. 



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 Mermithidce, 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 

 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. 



eggs and larva OP Mermis (enlarged). 



Arrow- Worms, — Order Ciletognatha. 



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 



