No. 392.] MWORTH-AMERICAN INVERTEBRATES. 649 
transference of the worms into herbivorous insects: (1) The 
second host, the carnivorous beetle, may die, and at its death 
the parasitic hair worm pass into a mass of decaying vegetation, 
and then be inadvertently swallowed by the cricket or grass- 
hopper; or (2) the may-fly larva dies, and the worm after pass- 
ing out of its body is swallowed by the orthopterous insect. In 
the first case the herbivorous insect would be the tertiary, in 
the second the secondary host. Probably at least one change 
of host always occurs, but there would seem to be no fixed regu- 
larity in regard to the sequence of hosts, nor in regard to the 
species of the host, for it would seem that embryos of the same 
species of hair worm are able to grow and develop in a variety 
of hosts. From the body cavity of the final host the worm, 
now nearly mature, but with its mouth stopped by a cuticular 
plug so that it can take no further nourishment, escapes in the 
water again, there to swim about for a time, and there finally 
to deposit its egg. We have seen that the final host is usually 
a terrestrial insect ; for the worm to reach the water to lay its 
eggs there, it is necessary that its host, by a rainstorm or flood, 
become drowned in a body of water. 
Probably but a small percentage of the hair worm larva ever 
arrives at the mature condition, since their transmission from 
host to host, and back to the water again, is so much a matter 
of environmental chance. There is opportunity for a great 
deal of study, with promise of interesting results, on the life 
history of these forms. By a wise provision of nature the 
genital products ripen prematurely, so that the individuals can 
reproduce themselves before they themselves are structurally 
adult. 
Hair worms in North America have been found in the nearly 
mature but still parasitic stage, in Orthoptera (crickets, grass- 
hoppers, Ceutophilus), in beetles (rapacious genera, such as 
Harpalus), and (rarely) in spiders and Lumbriculus. In other 
lands they have been found in other groups of insects, in snails, 
rarely in vertebrates, where their presence is probably purely 
accidental, as it certainly is in man. In the mature free state 
they occur in small ditches, small streams, sometimes springs 
(as Gordius lineatus), and large lakes. They appear to be very 
