154 
HALF HOURS WITH INSECTS. 
[Packard. 
No Myriopods are aquatic, but a number of mites and 
allied forms live in water and extract tlie air mechanically 
mixed with the water, without having to rise to the surface. 
They have two spiracles and air tubes, but how they extract 
the air in the water is not known. Such are the Hydrachna 
and Atax, which live in their early stages as parasites be¬ 
tween the gills of fresh water clams, while some species 
attach themselves to water insects. 
Of the various modes of swimming among insects, the 
Fig. 121. 
Fig. 122. 
Macromia transversa. 
simplest, though not the most graceful, is wriggling. By a 
series of contortions of the body the young Chironomus 
moves about without much apparent purpose. The twist¬ 
ings and turnings of the larval mosquito are anticipations in 
nature of the most laborious and complicated feats in gym¬ 
nastics of the circus clown. The latter realizes the amount 
of muscular exertion and nervous strain expended in a two- 
minutes circumtorsion of the ring. The young mosquito, 
through its life of such violent undulations, knows no fatigue. 
A study, through the transparent skin, of the arrangement 
26 
